Note: Descriptions are shown in the official language in which they were submitted.
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STD 442 PB - 1 -
SECURITY DOCUMENT
10
Background of the Invention
The importance of making various types of documents safe
from nefarious duplication is readily apparent. The
development of the color copier has resulted in significant
concern in this regard. The quality of color reproductions
that can be made with a color copier has become so good that
it may be very difficult to distinguish original documents
from color reproductions. Even if a reproduction is not an
exact copy, the reproduction often appears reasonably
authentic in the absence of the original for comparison
purposes. As a consequence, there has been concern that color
copiers could be used to reproduce security documents, such as
checks, stock certificates, automobile title instruments, and
other documents of value, for illegal purposes. This concern
has been heightened with the advent of desk top publishing
software and hardware, including personal computers and
scanners. Such desk top publishing systems allow
sophisticated image processing and printing not previously
generally available.
Many techniques have been developed to prevent improper
reproduction of security documents. One of the most
successful is the use of a hidden warning message which is
readily apparent on reproduced copies of a document, but which
is invisible, or nearly so, on the original document.
Examples of this technique are shown in U.S. Patent Nos.
4,227,720 and 4,310,180. A single tone warning phrase and a
single tone background pattern are used. Tone refers to the
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STD 442 PB -
visual effect produced by solid ink coverage or by halftone
dots, bars, or marks which cover a portion of a printed area
and which usually have a frequency that is measured in dots,
lines, or marks per inch. Halftone dots, bars, or marks may
be more or less uniformly distributed over an area to produce
the visual effect, i.e., less than full tone, of a lighter
overall color with the use of a darker color ink printed at
less than full area coverage. The warning phrase and
background pattern area tones are of different frequencies and
are made up of dots, bars, or marks of different sizes, but
they are selected to provide similar appearance to the eye of
a casual observer. A less than full tone effect may also be
produced by full area coverage of a paler color of ink than
the darker color of ink used for the halftone dots, bars, or
marks.
Because the tone of the warning phrase and the tone of
the background pattern surrounding the warning phrase on the
original document are selected to be the same, these two areas
have much the same visual impact on an observer, and the
warning phrase is not readily perceived. The optics of color
copiers have typically been unable to reproduce relatively
small halftone dots, lines or other elements. As a
consequence, reproduced copies of the original document will
have a noticeable warning phrase.
A camouflage pattern is sometimes utilized to obscure the
warning phrase further. The camouflage pattern may be defined
by areas in which the dots, bars, or marks have been deleted
from both the warning phrase and the background pattern. The
camouflage pattern may also be defined by a pattern of dots,
bars, or marks which are smaller than or larger than those
used in the background pattern and the warning phrase, or by
areas of complete coverage of a paler ink. The patterns of
such camouflage images have commonly been decorative, although
some camouflage images have been utilized which identify the
organization producing the document. Such a camouflage image
may, for example, be a variation of the company logo, or
letters spelling out the name of the company.
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STD 442 PB - 3 -
In recent years, color copiers have been improved
substantially. These new color copiers have made the above
technique less effective in protecting documents. By
manipulating the control settings on such copiers, copies can
be made of such documents in which the warning phrase does not
appear on reproductions when some of the most commonly used
frequency and size combinations are used. Furthermore, desk
top publishing systems now available in conjunction with laser
printers, offer additional possibilities for unauthorized
copying. Therefore, it is clear that improvements in this
technique are desirable.
One such improvement is shown in U.S. Patent No.
4,351,547, which also utilizes a single tone background and a
single tone cancellation phrase. In this improved technique,
the warning phrase is not defined by dots or elements of the
same size and frequency. Instead, the warning phrase is
defined by an alternating element pattern which includes large
elements of lower frequency than the background tone, and
small elements located in exact registry with the large
elements.
U.S. Patent No. 4,579,370 represents another improvement
in the use of a hidden warning phrase. The background and
warning phrase are each made up of halftone elements of two
pairs of element sizes. For example, the background might be
made with about 50% of 130 lines per inch, .005 inch diameter,
and the balance of 130 lines per inch, .006 inch diameter; the
cancellation term might be made with about 500 of the elements
of 65 lines per inch, .010 inch diameter and the balance of 65
lines per inch, .012 inch diameter. This provides additional
protection for documents against improper copying.
These methods have generally been successful in
protecting documents at most copier settings. However, by
adjusting the settings for sharpness and lightness/darkness it
has still been possible on some copiers for a skilled
individual to produce a copy in which the warning phrase is
not visible.
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STD 442 PB - 4 -
Furthermore, while the technique of hiding a cancellation
or warning phrase within a background image has provided an
indication on the face of copies that they are not original
documents by indicating "VOID" or the like, there has been no
corresponding indication on the original documents that they
are in fact original. Rather, the recipient relied on an
assessment of the overall appearance of the document, and the
fact that it did not bear a visually apparent cancellation
phrase or warning phrase as indications of authenticity.
Therefore, there remains a need in the art for a security
document which provides improved protection against copying
over a wide range of copier settings, or against manipulation
using desk top publishing systems.
Summary of the Invention
These needs are met by a security document according to
the present invention which includes a document substrate
having a surface for receiving printed indicia. A half-tone
warning image is printed in first areas on the surface. The
warning image comprises at least one word indicating that a
copy of the document is not an original document. A half-tone
background image is printed in second areas on the surface.
The second areas surround the first areas. Finally, a
camouflage image extends over the document surface; the
camouflage image confuses the eye of an observer such that the
warning image is not readily observed. The camouflage image
comprises at least one word indicating to an observer that the
document is an original document. As will become apparent,
the half-tone warning image indicates the status of a copy of
the document, whereas the camouflage image indicates the
status of the original document. One of the half-tone warning
images and the half-tone background images is printed with
half-tone elements of such a line spacing and element size
that it is not readily reproducible by a copier. As a
consequence, the half-tone warning image becomes apparent on a
copy of an original document.
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STD 442 PB - 5 _
The camouflage image is defined by portions of the first
areas in which half-tone elements are not printed.
Alternatively, the camouflage image may be defined by portions
of the second areas in which half-tone elements are not
printed. Further alternatively, the camouflage image may be
defined by portions of the first and second areas in which
half-tone elements are not printed.
The warning image and the camouflage image may comprise
words which are antonyms. Such words may include INVALID and
VALID, UNAUTHORIZED and AUTHORIZED, COPY and ORIGINAL, VOID
and VALID, and DUPLICATE and ORIGINAL, for example. By "word"
is meant written indicia of any sort, including any
recognizable character or symbol.
The sizes of the half-tone elements making up the warning
image and the background image may vary across the surface
such that the density of the warning image and the density of
the background image vary together across the surface, thereby
impeding copying the security document without the warning
image being apparent on at least some portion of the copy of
the security document, regardless of the copier setting
adjustments that may be made.
The warning image may be substantially larger than the
camouflage image, and the camouflage image may be repeated a
plurality of times over the warning image. The letters of the
word making up the camouflage image are preferably outlined by
areas in which no half-tone elements are printed.
Accordingly, it is a object of the present invention to
provide a security document in which a half-tone warning image
is printed on the original document but does not become
apparent except on copies that are made of the original
document; to provide such a security document in which the
half-tone warning image is obscured to the eye of an observer
by a camouflage image, such camouflage image indicating the
authentic status of the original security document; and to
provide such a security document in which the half-tone
warning image and the camouflage image consist of words that
are antonyms.
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STD 442 PB
Other objects and advantages of the invention will be
apparent from the following description, the accompanying
drawings and the appended claims.
Brief Description of the Drawings
Fig. 1 illustrates a check according to the present
invention as it would appear to a casual observer;
Fig. 2 is an enlarged portion of the check of Fig. 1;
Fig. 3 is an illustration of two different areas on the
surface of the document, greatly enlarged;
'Fig. 4 illustrates the appearance of a reproduction of
the document of Fig. 1 obtained on a color copier or desk top
publishing system;
Fig. 5 is a drawing, similar to Fig. 4, illustrating the
appearance of a reproduction obtained on a color copier or
desk top publishing system at different control settings;
Fig. 6 is a drawing, similar to Fig. 4, illustrating the
appearance of a reproduction obtained on a color copier or
desk top publishing system at other control settings;
Fig. 7.is an illustration of an alternate embodiment of
the present invention;
Fig. 8 is an illustration of another embodiment of the
present invention;
Fig. 9 is an illustration of an alternate embodiment of
the present invention;
Fig. 10 is an illustration of another embodiment of the
present invention;
Figs. 11, 12 and 13 illustrate another embodiment of the
present invention;
Fig. 14 illustrates graphically the changes in image
density of yet another embodiment of the present invention;
Figs. 15 is an illustration of another embodiment of the
present invention;
Fig. 15A depicts the appearance of a copy of the document
of Fig. 15 obtained on a color copier or desk top publishing
system; and
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STD 442 PB - '7 -
Fig. 16 is an illustration of yet another embodiment of
the present invention.
Detailed Description of the Preferred Embodiment
Fig. 1 illustrates a check 10 made according to the
present invention, as seen by a casual observer, with a
lighter tone area, first part 20, and a darker tone area,
second part 22. The lighter appearance of first part 20 is
due to smaller element size which results in a smaller
percentage of the area of first part 20 that is covered with
ink compared to second part 22. The second part 22 is shown
as defining a complete border around first part 20. However,
it may form only a partial border. It will be appreciated
that the first part 20 may be darker than the second part 22,
if desired.
Fig. 2 is a detailed illustration of a portion of check
10. Fig. 2 shows sections of first part 20 and second part
22. First part 20 contains elements of a first half-tone
background image 30 and first warning phrase or half-tone
warning image 32. The elements of first background matter 30
are illustrated as being smaller than those of first half-tone
warning image 32, but they could be larger, as well.
Second part 22 has elements of a second half-tone
background image 34 and second half-tone warning image 36.
The elements of a second half-tone background image 34 are
represented as being smaller than those of second half-tone
warning image 36; alternatively, they could be larger,
however. The elements of second half-tone background image 34
are represented as being larger than those of first half-tone
background image 30, and the elements of second half-tone
warning image 36 are shown as being larger than those of first
half-tone warning image 32. However, they could be smaller.
The frequencies of the elements in the first and second
half-tone background image may be the same or they may be
different. Similarly, the frequencies of the elements of the
first and second background terms may be the same or
different. For instance, one useful combination would be 130
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STD 442 PB - g -
lines per inch at 10% and 65 lines per inch at 15o in the
first part, and 130 lines per inch at 20o and 65 lines per
inch at 25o in the second part. Another useful combination
might be 130 lines per inch at loo and 65 lines per inch at
15o for the first part, and 120 lines per inch at 20o and 60
lines per inch at 25o in the second part.
Phantom dotted lines 40 do not actually appear on the
check. They have been used merely to show the edges of the
camouflage image 38. The camouflage image may be defined by
the absence of the elements of the first and second half-tone
background images and first and second half-tone warning
images. It may also be defined by the presence of elements of
a larger or smaller size than the background elements.
Fig. 3 shows an enlarged view of an area of the first
part 20 and second part 22 on a different security document.
The camouflage image 38 consists of wavy lines on the
illustrated document. The elements of the first half-tone
background image 30 are smaller than the elements of first
half-tone warning image 32. The elements of second half-tone
background image 34 are smaller than the elements of second
half-tone warning image 36, but larger than the elements of
first half-tone background image 30. The elements of second
half-tone warning image 36 are larger than the elements of
first half-tone warning image 32.
The frequency of the elements of the first half-tone
background image 30 is the same as the frequency of the
elements of the second half-tone background image 34. The
frequency of the elements of first and second half-tone
warning images 32 and 36 is the same, and it is less than that
of first and second half-tone background image 30 and 34.
The relationship between the size and frequency of the
elements explains the difference in the appearance of the two
parts. First part 20 appears to be lighter in tone than
second part 22 because there is a lower percentage of the
document surface covered with ink in relation to the total
area of the document surface in first part 20; first part 20
is therefore of a lighter tone than second part 22. This is
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STD 442 PB - g -
advantageous in that if a copier is adjusted to obscure or
eliminate a half-tone warning image in first part 20 of a
copy, the half-tone warning image in the second part 22 will
appear on the reproduced copy. Similarly, if the copier is
adjusted to obscure or eliminate the half-tone warning image
in the second part 22 of the copy, the half-tone warning image
in first part 20 will appear on the reproduced copy.
It should be appreciated that the tone of an area of a
document, that is the darkness or lightness of the document as
it appears to the eye of an observer, is not a function of
only density of the halftone printing elements. It is true,
however, that with a halftone screen of a given number of
lines per unit length, a greater density which results from
larger halftone elements will produce a darker tone. It has
been found, however, that an area having large, widely spaced
elements will appear lighter in tone than another area having
smaller, more closely spaced elements, even though the amount
of document surface covered by ink per unit area is the same
in each instance.
Figs. 4, 5, and 6 represent the results of various
attempts to copy the check 10 of Figs. 1 and 2 on a color
copier. In Fig. 4, when the copier is adjusted to obscure
half-tone warning image 44 in second part 22, half-tone
warning image 42 in first part 20 appears clearly on the
reproduced copy.
In Fig. 5, if the copier is adjusted to lighten the copy
to eliminate half-tone warning image 42 in first part 20, the
adjustment produces a copy in which half-tone warning image 44
in second part 22 is clearly visible on the reproduced copy.
Finally, in Fig. 6, when the copier is adjusted to obscure
half-tone warning image 42 in first part 20 of the reproduced
copy, half-tone warning image 44 in second part 22 is readily
apparent on the reproduced copy.
Fig. 7 shows an alternative embodiment of the present
invention. The check 50 contains elements of a half-tone
background image, elements of a half-tone warning image, and a
camouflage image as illustrated above in respect to Figs. 1-6.
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STD 442 PB - 10 -
The tone of the elements varies across the face of the check
50. It could decrease from left to right as shown. This may
be accomplished by varying the size of the halftone elements,
their spacing, or both, across the face of the check 50.
Other variations are possible.
Fig. 8 illustrates diagrammatically yet another
embodiment of the present invention. In this embodiment, the
frequencies of the elements of the half-tone background image
and the half-tone warning images remain the same, while the
size of the elements is varied across the document. This is
called a graded screen. For example, the frequency might be
130 and 65 lines per inch for the half-tone background image
and the half-tone warning image, respectively. The size of
the elements of the half-tone background image may vary across
the document from 500 of the area covered to 50, and the half-
tone warning image may vary across the document from 60% to
7%. In the illustrated document, the highest percentages of
coverage are at the top of the document. These percentages
are gradually reduced toward the bottom of the document. The
illustrated document shows this change in coverage percentages
as occurring in steps, producing bands of slightly different
tone. If desired, however, the size of the elements may be
continuously varied over the document surface. Regardless of
the manner in which the element size of the half-tone
background image and the element size of the half-tone warning
image are varied, the selection of element sizes for a given
area on the document is made such that they provide
substantially equal tone.
The address area 60 and the amount area 62 are made of
halftone elements which are substantially the same spacing as
the background elements. These areas may contain the
camouflage image or the image may be omitted. The address
area 60 and the amount area 62 are readable by image scanners.
Fig. 8 also shows a quality control target 69 printed on the
surface of the check. The quality control target comprises a
high density area 70, a low density area 72, and an
intermediate density area 74. Warning bands 76 of high
STD 442 PB - 11 -
density printing may be positioned at the top and bottom of
the check 50 as shown. The low density printing may be used
for portions such as the address and amount areas 60 and 62.
Intermediate targets 75 may be provided in obscure areas of
the form and printed without the camouflage image.
Fig. 9 illustrates diagrammatically yet another
embodiment of the present invention, with parts of the
document corresponding to those of Fig. 8 being labeled with
like reference numerals. In the embodiment of Fig. 9, the
frequencies of the elements of the half-tone background image
and the half-tone warning images are constant, while the size
of the elements is varied across the document. In contrast to
the embodiment of Fig. 8, however, the highest percentages of
coverage by screen elements occurs at both the top and bottom
of the document. The percentages are gradually reduced toward
a central band 80 of generally uniform tone. As with Fig. 8,
Fig. 9 shows the changes in percentage coverage occurring in
steps, producing bands of slightly different tone. If
desired, however, the size of the elements may be continuously
varied over the document surface. Once again, the selection
of element sizes for given areas on the document is made such
that they provide substantially equal tone.
Fig. 10 illustrates diagrammatically a further embodiment
of the present invention, with parts of the document
corresponding to those of Fig. 8 being labeled with like
reference numerals. In the embodiment of Fig. 10, the
frequencies of the elements of the half-tone background image
and the half-tone warning images are constant, while the size
of the elements is varied across the document. In contrast to
the embodiment of Fig. 9, the embodiment of Fig. 10 does not
include a central band of generally uniform tone. Rather the
percentage of coverage by the screen elements gradually
decreases from the top and bottom of the document to the
middle of the document. As with the other embodiments, the
selection of element sizes is made such that the half-tone
background image and the adjacent portions of the half-tone
warning images are of substantially equal tone.
STD 442 PB - 12 -
It should be understood that the phrase "half-tone
warning image" is intended to include not only words such as
the word "VOID" shown in the drawings, but also words and
phrases which simply make evident to an observer that the
document being inspected is a copy of the original document.
Such phrases as "PHOTOCOPY", "COPY", and "DUPLICATE" may be
used for this purpose.
The present invention may be incorporated in a number of
different security documents of varying design. Figs. 11-13
illustrate yet another embodiment of the present invention.
Fig. 11 shows the improved security document 70 with all
alphanumeric printed matter removed, leaving only the half-
tone background image, the half-tone warning image, and the
camouflage image printed on the substrate 72 having a surface
for receiving printed indicia. The half-tone background image
consists of a pattern of elements of a first size and a first
frequency such that the half-tone background image is printed
at a first density perceived by an observer as a first tone.
The half-tone warning image consists of a pattern of elements
of a second size and a second frequency such that the half-
tone warning image is printed at a second density perceived by
an observer as a second tone. As discussed more fully below,
the first and second tones may generally be the same across
the face of the security document. As with the embodiments
previously discussed, elements of one of the first size or the
second size are sufficiently small such that they are not
reproduced by a color copier at a particular copier setting,
and elements of the other of the first size or the second size
are sufficiently large such that they are reproduced by the
color copier at the particular copier setting. As a
consequence, a copy of the security document made on a color
copier displays the half-tone warning image.
In this embodiment, the security document surface is
divisible into a plurality of bands extending across the
surface. This is more clearly shown in Figs. 12 and 13, with
the bands being designated by reference numerals 74 through
82. The document is illustrated with the entire surface
STD 442 PB - 13 -
divided into bands, but it should be understood that only a
portion of the surface may be divided in this manner, if
desired. Furthermore, the document is illustrated with the
bands extending across the entire width of the document. If
desired, however, other arrangements, such as non-parallel
bands, extending radially outward from a common point, may be
utilized. Fig. 12 illustrates the document of Fig. 11 as it
would appear without the camouflage image, while Fig. 13
graphically depicts the change in densities of the areas
printed with the first and second size elements. Note that
the sizes of the elements of the first and second sizes vary
across each of the bands. As a consequence, the density of
the half-tone background image and the density of the half-
tone warning image vary together across each of the bands on
the surface in a direction generally normal to the bands. By
this arrangement, copying the security document without the
half-tone warning image being apparent on at least some
portion of the copy is impeded. It should be appreciated that
in some instances the size of the elements of the first and
second sizes will vary across less than all of the bands.
The camouflage image, defined by the absence of the
elements of the first and second sizes in a pattern simulating
blocks, disguises the half-tone warning image quite well. The
degree to which this disguise is successful can be easily seen
by comparing Figs. 11 and 12.
It should be appreciated that any of a wide variety of
camouflage images may be utilized in this fashion to disguise
the half-tone warning images on a security document according
to the present invention. For a camouflage to be effective,
the camouflage image usually occupies about 50% of the
document surface area. A properly configured camouflage image
becomes the dominant image in the eye of the casual observer.
Although a camouflage image defined by the absence of elements
is shown in Fig. 11, it will be understood that a camouflage
image may also be defined by the presence of further elements.
As is apparent from Fig. 12, the half-tone warning image
consists of a plurality of letters, each of which is
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STD 442 PB - 14 -
approximately two bands in height. Actually, a plurality of
half-tone warning images are printed, with each half-tone
warning image being printed over an associated pair of the
plurality of bands. Specifically, the half-tone warning image
consists of the word 'VOID" repeated numerous times along each
of the bands 74-82. Although the x-axis of Fig. 13 is not
drawn to scale, it will be appreciated that the plurality of
half-tone warning images and the plurality of bands 74-82 vary
in height. Band 79 is generally twice as high as the other
bands.
A careful inspection of Fig. 12 reveals that while the
tone of the half-tone background image and the tone of the
half-tone warning image are generally the same at each point
on the document, still some differences between the tone of
the half-tone background image and the tone of the half-tone
warning image do exist. The density of each portion of the
surface printed with those elements which are sufficiently
large such that they are reproduced by the color copier at the
particular copier setting is greater than the density of
adjacent portions of the surface printed with elements which
are sufficiently small such that they are not reproduced by a
color copier at the particular copier setting. These
differences in tone and density enhance the ability of the
security document of the present invention to impede copying
without the half-tone warning image being apparent on a least
some portion of the copy. Even with these differences in
density and tone, however, the half-tone warning images are
sufficiently obscured by the camouflage image so as not to be
apparent to the eye of a casual observer. It will be
appreciated, however, that if desired the densities may be
selected such that the tone of the half-tone background image
and the tone of the half-tone warning image are the same at
each point on the document.
As will be noted from a review of Fig. 13, the density of
the half-tone background image and the density of the half-
tone warning image vary together linearly across each of the
plurality of bands. In some cases, however, the density of
STD 442 PB - 15
the half-tone background image and the density of the half-
tone warning image will vary together only across some of the
plurality of bands. In the illustrated document, the half-
tone background image is printed with a 130 line per inch,
halftone dot screen, and the half-tone warning image is
printed with a 65 line per inch, halftone dot screen. The
density of the half-tone warning image in band 74 is 1000,
meaning full ink coverage at the top of the band, and drops to
70% at the bottom of the band. Similarly, the density of the
half-tone background image in band 74 is 70% at the top of the
band, and drops to 42o at the bottom of the band. Note that
the density of the half-tone warning image in band 75 is 70%
at the top of the band and drops to 55o at the bottom of the
band. Similarly, the density of the half-tone background
image in band 75 is 42% at the top of the band, and drops to
36o at the bottom of the band. The density of the half-tone
background image and the density of the half-tone warning
image along each edge of each of the bands 74 through 82 are
substantially the same as the density of the half-tone
background image and the density of the half-tone warning
image along the edges of the adjacent bands, respectively. As
a consequence, the transition from one band to the next is
accomplished in a manner that is not readily apparent to a
casual observer.
The density of the security document may be varied in
other ways. The density of the half-tone background image and
the density of the half-tone warning image vary together in a
non-linear fashion across at least some of the bands.
Reference is made to Fig. 14, which illustrates the density
changes in the half-tone background image and the half-tone
warning images of a security document having eight bands 83-
90. Band 83 extends across the top edge of the document and
band 90 extends across the bottom edge of the document. In
this example, the heights of the bands for a document which is
the size of a typical check are as follows.
STD 442 PB - 16 -
Band Heiaht (inches)
83 .175
84 .200
85 .450
86 .475
87 .500
88 .450
89 .225
90 .211
In this example, the half-tone background image is printed
with a 130 line per inch, halftone dot screen at a 45° screen
angle, and the half-tone warning image is printed with a 65
line per inch, halftone dot screen at a 45° screen angle. The
density values are as follows.
Band Half-tone A half-tone
num- warning background
image image
ber
Taper Start Stop Direct Taper Start Stop Direct
83 LIN 55 70 90 LIN 36 42 90
84 LOG 35 55 90 LOG 25 36 90
85 LOG 35 20 270 LOG 25 14 270
86 LOG 20 12 270 LOG 14 7 270
87 LIN 12 7 270 LIN 7 5 270
88 LIN 11 7 90 LIN 6 5 90
89 LOG 17 11 90 LOG 11 6 90
90 LOG 17 26 270 LOG 11 16 270
In this table, the abbreviations used are as follows.
"Taper" indicates the type of change of the
graduated screen between the start and the stop
values. LIN indicates an equal change for
equal distance increments between the start and
stop boundaries. LOG indicates a more rapid
change for equal distance increments closer to
the start boundary and becoming progressively
213~~9'~
STD 442 PB - 17 _
less closer to the stop boundary. It should be
noted that the density of the half-tone
background image and the density of the half-
tone warning image vary together in a
logarithmic manner across at least some of the
plurality of bands.
"Start" is the screen percentage selected to
start the band. It may be at the top or bottom
of the band depending on the direction of
taper.
"Stop" is the screen percentage selected to end
the band. It may be at the top or bottom of
the band depending on the direction of taper.
"Direct" is the direction of change in element
sizes between the start and stop boundaries. A
notation of 270 means that the values change
from the start value at the top of the band to
the stop value at the bottom of the band. A
notation of 90 means that the values change
form the start value at the bottom of the band
to the stop value at the top of the band.
In a preferred embodiment of the present invention, ten
bands 200-209 are provided, extending laterally across the
document, with the density values being set as follows.
Band Half-tone A half-tone
num- warning background
image image
ber
Taper Start Stop Direct Taper Start Stop Direct
200 LOG 32 46 90 LOG 21 29 90
201 LIN 32 23 270 LIN 21 14 270
202 LIN 23 14 270 LIN 14 08 270
203 LIN 14 08 270 LIN 08 04 270
204 LOG 08 06 270 LOG 04 03 270
205 LOG 07 06 90 LOG 04 03 90
206 LIN 11 07 90 LIN 05 04 90
207 LIN 16 11 90 LIN 09 05 90
208 LIN 24 16 90 LIN 13 09 90
209 LIN 33 24 90 LIN 19 13 90
STD 442 PB - lg -
It is preferred to prepare the images that are subsequently
printed on a security document using a personal computer and
drafting software entitled FREEHAND 3.1, available from Aldus
Co. This software permits the boundary densities to be
precisely controlled. It is preferred that the images are
then printed out from the personal computer using an imager
having 3000 dots per inch, or greater, resolution. Using
these printed images, printing of the security documents is
then accomplished in a conventional manner, taking care to
follow good commercial printing practices to produce a quality
image. This includes using quality inks that are dense in
color and that do not produce undue dot gain.
If desired, a security document according to the present
invention may be printed in more than one color ink. It has
been found to be desirable to print the upper or lower bands
of a document with a blue ink, and the remaining bands with a
green ink. With a document in which the tone becomes
progressively lighter toward the center portion of the
document, the transition from blue to green is very subtle,
and the color of the half-tone background image and the color
of the half-tone warning image appear to vary together over
the surface. This technique permits the printing of a
document in which a gradual blending of the colors is
approximated.
To facilitate the blending of colors, overlapping of
areas printed with the two colors is accomplished. As an
example, if the upper half of a document is printed with blue
ink and the lower half of the document is printed with green
ink, the bottom band of the upper half of the document may
also be printed with green ink. Preferably, this bottom band
is printed only with smaller elements, and the screen angle of
these smaller elements differs from the screen angle of the
elements printed in blue ink. For example, elements printed
in blue ink may have a screen angle of 90°, whereas elements
printed in green ink may have a screen angle of 45°. A
similar arrangement is provided for the upper band of the
bottom half of the document. By this technique, the blue and
21~8~°~
STD 442 PB - 19 -
green elements are, for the most part, not printed on top of
each other, and both colors are visible.
It will be appreciated that differing arrangements may be
utilized within the scope of the present invention to cause of
the tone of the half-tone background image and the tone of the
half-tone warning image or terms to vary across at least some
of the bands. For example, in another embodiment the sizes of
the elements of the first and second sizes may vary across
each of the bands and the frequencies of the elements of the
first and second frequency may vary across each of the bands.
In this embodiment, the density of the half-tone background
image and the density of the half-tone warning image vary
together across each of the bands on the surface in a
direction generally normal to the bands. In yet another
embodiment, only the frequencies of the elements of the first
and the second frequency varying across at least some of the
bands such that the density of the half-tone background image
and the density of the half-tone warning image vary together
across at least some of the bands on the surface in a
direction generally normal to the bands.
It will be further appreciated that it may be desirable
in some instances to provide an area of the document of the
present invention with a half-tone background image and half-
tone warning images that do not vary in tone. This may be the
case, where a uniformly light tone is desired to facilitate
reading information that is to be printed later in this area.
Further, it may be desirable in some instances to provide an
area of the document without any of the larger sized elements
that make up either the half-tone background image or the
half-tone warning images. This may be the case where it is
desired to print machine readable characters in this area, and
the larger elements may impede character recognition.
Reference is now made to Figs. 15 and 15A, which
illustrate yet another embodiment of the present invention.
It will be appreciated that these figures are not drawn to
scale; rather, for purposes of clarity, the half-tone elements
have been illustrated as larger and more widely spaced than
~~~~0~7
STD 442 PB - 20 -
would actually be the case. As seen in Fig. 15, the security
document 100 includes a document substrate 102 having a
surface 104 for receiving printed indicia. A half-tone
warning image 106 is printed in first areas 108 on the surface
104. The warning image 106 consists of at least one word
indicating that a copy of the document is not an original
document. In the example shown in Fig. 15, the warning image
106 consists of the letters making up the word ~~VOID~~. A
half-tone background image 110 is printed in second areas 112
on the surface 104 which surround the first areas 108. Either
the half-tone warning image 106 or the half-tone background
image 110 is printed with half-tone elements of such a line
spacing and element size that it is not readily reproducible
by a copier. As a result, the half-tone warning image 106
becomes apparent on photocopies of the original document that
may be made, either as a positive image or as a reverse image.
In the embodiment of Fig. 15, the half-tone warning image 108
is printed with half-tone elements that are not readily
reproducible by a copier.
The embodiment of Fig. 15 is shown as having relatively
large dots making up the background image 110, perhaps at a
line screen of 65 lines per inch, and relatively small dots
making up the half-tone warning image 106, perhaps at a line
screen of 130 lines per inch. The densities of the half-tone
background image and the half-tone warning image are selected
to provide generally the same tone for the two images on the
original document. Thus, the warning image 106 on the
document 100 is not apparent to the eye of a casual observer.
To obscure the warning image even further, a camouflage image
114 is provided. Camouflage image 114 extends over the
document surface 102 for confusing the eye of an observer such
that the warning image 106 is not readily observed. The
camouflage image 114 of this embodiment performs the
additional function of indicating to an observer that the
document is an original document. The camouflage image 114
preferably comprises at least one word that provides this
indication.
,.. '
STD 442 PB - 21 -
In the illustrated example, the camouflage image 114
comprises the word "VALID" which is repeated across the
document surface. The camouflage image 114 may be defined by
portions of the first and second areas 108 and 112,
respectively, in which half-tone elements are not printed, as
shown by Fig. 15. Alternatively, the camouflage image 114 may
be defined by portions of only the first areas in which
half-tone elements are not printed, or by portions of only the
second areas in which half-tone elements are not printed.
Note that the camouflage image message, "VALID," is quite
prominent in Fig. 15. Thus the recipient of the security
document 100 is given confidence in the authenticity of the
document. Not only does the recipient not see an indication
of invalidity, but the recipient sees a positive indication
that the document is valid. When a copy is made of the
document, such as for example a copy on a color copier, the
elements making up the half-tone warning image 106 are
sufficiently small that they are not adequately reproduced on
the copy, and may not copy at all. As a consequence, the
warning image "VOID" appears prominently on the photocopy, as
illustrated in Fig. 15A, telling the recipient that the
document is not an original document. As will be noted from
Figs. 15 and 15A, the camouflage image "VALID" is repeated a
plurality of times over the larger warning image "VOID." The
warning image 106 is substantially larger than the camouflage
image 114. By this arrangement, the word VALID is
sufficiently prominent on the original document to be easily
noticed by a casual observer, yet the warning image VOID
predominates the photocopy of the document, even if remnants
of the camouflage image may be found in the second areas 112.
A wide array of words are available to convey the
information that the original document is an original, and
that the photocopy of the document is a copy. It is
preferable, of course, that the word used for the warning
image and the word used for the camouflage image be antonyms.
Word pairs such as "INVALID" and "VALID," "UNAUTHORIZED" and
"AUTHORIZED," "COPY" and "ORIGINAL," "VOID" and "VALID," and
'_
STD 442 PB - 22 -
"DUPLICATE" and "ORIGINAL," may be used for the warning image
and the camouflage image, respectively. Other word pairs may
also be utilized, including word pairs in which the words have
dissimilar, but not necessarily opposite meanings, such as for
example "COPYRIGHT VIOLATION" and "ORIGINAL." Further,
symbols and other indicia may be employed as "words" within
the context of the present invention.
If desired, the sizes of the half-tone elements making up
the warning image and the background image may vary across the
surface of the security document such that the density of the
warning image and the density of the background image also
vary together. In such an instance, the security document
will have the same general appearance as that shown in Fig. 7,
with the exception, of course, that the camouflage image will
clearly advise the observer of the authenticity of the
document. While it is preferred that the change in image tone
across the document be accomplished by varying the size of the
halftone elements, it may also be effected by varying their
spacing, or by varying both their size and their spacing
across the face of the document. Regardless of the manner in
which the varying tone document is produced, such a document
is more difficult for a forger to copy without the warning
image being apparent on at least some portion of the copy.
Reference is now made to Fig. 16, which shows another
embodiment of the security document of the present invention.
In this embodiment, the same reference numerals are used as in
the embodiment of Fig. 15 to designate like elements. The
security document 100 includes a document substrate 102 having
a surface 104 for receiving printed indicia. A half-tone
warning image 106 is printed in first areas 108 on the surface
104. The warning image 106 consists of at least one word
indicating that a copy of the document is not an original
document. The warning image 106 consists of the letters
making up the word "VOID" in outline form. A half-tone
background image 110 is printed in second areas 112 on the
surface 104 which surround the first areas 108.
.-- 2~'~80
STD 442 PB - 23 -
The embodiment of Fig. 16 is shown as having relatively
small dots making up the background image 110, perhaps at a
line screen of 130 lines per inch, and relatively large dots
making up the half-tone warning image 106, perhaps at a line
screen of 65 lines per inch. A camouflage image 114 extends
over the document surface 102 and confuses the eye of an
observer such that the warning image 106 is not readily
observed. Note that the camouflage image does not extend
through the warning image. The elements making up the warning
image are sufficiently separated, however, that this is not
readily apparent. As with the previous embodiment, the
camouflage image 114 performs the additional function of
indicating to an observer that the document is an original
document. The camouflage image 114 preferably comprises at
least one word that provides this indication.
As is apparent from Fig. 16, the letters of the word
making up the camouflage image 114 are outlined by areas in
which no half-tone elements are printed. This use of outline
letters as a camouflage is effective in that in those cases in
which the camouflage image extends across the areas having the
larger elements, the remnants of the camouflage image are less
apparent on the copy of the document. This is preferable, of
course, since it is desired that the camouflage image word be
prominent on the original document and unnoticed on the copy
of the document, if possible.
Having described the improved security document of the
present invention in detail and by reference to different
embodiments thereof, it will be apparent that certain
modifications and variations are possible without departing
from the scope of the invention defined in the appended
claims.
