Patent Publication Number: US-6665406-B1

Title: Variable density verification

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. application Ser. No. 09/046,571, now U.S. Pat. No. 6,396,927 filed on Mar. 23, 1998, which is a continuation-in-part-of U.S. application Ser. No. 08/602,243, filed on Feb. 16, 1996, now U.S. Pat. No. 5,873,604, which is a continuation-in-part of U.S. application Ser. No. 08/450,975, filed on May 25, 1995, now U.S. Pat. No. 5,704,651, and U.S. application Ser. No. 08/568,587, filed on Dec. 7, 1995, now U.S. Pat. No. 5,772,248. The disclosures of each of these prior applications are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention pertains to the field of security systems for documents, including more particularly to novel duplication resistant documents and methods of creating duplication resistant documents. 
     BACKGROUND 
     The importance of making documents safe from duplication and alteration is readily apparent. The advent of improved photocopy equipment, particularly high resolution color photocopy equipment, as well as desk top publishing and digital scanning, has provided the unscrupulous with the means for unauthorized duplication of original documents for the purpose of passing them off, with or without alteration, as the original document. The quality of the reproductions obtainable through these means is so good that, it is difficult to distinguish original copies from color reproductions. Even if the duplication is not exact, the reproduction often appears authentic in the absence of the original for comparison. This problem is well known to the issuers of such original documentation, and considerable attention has been given to find ways and means to prevent unauthorized duplication of such documents by photocopiers or other electronic methods. 
     Many techniques have been developed to prevent improper reproduction of original documents. One of the more known techniques is based on the phenomenon that photographic copiers have an element value (sometimes referred to as element frequency) threshold above which the photocopier is unable to distinguish the individual elements of the pattern of for example, halftone printing. In general, a pattern with a low line screen value of large sized elements is more easily reproducible than a pattern with a high line screen value of small sized elements. 
     In accordance with this technique, a hidden warning message, such as “VOID” or “COPY,” is printed in a halftone over a halftone background printed on a substrate. The line screen value of the hidden warning message is selected, such that the halftone elements of the hidden warning message are reproduced when photocopied. The line screen value of the background; however, is selected, such that, the halftone elements of the background are not reproduced when photocopied. As a result, the hidden warning message will appear on duplicates of the original document made by photocopying. This method is also used by reversing the halftones of the hidden warning message and the background such that the elements of the hidden warning message are not reproduced and the elements of the background are reproduced when photocopied or scanned. Known line screen values that are used to print these types of hidden warning messages and backgrounds are, e.g., 65 LPI and 133 LPI, respectively (i.e., a line screen value ratio of approximately 2.) 
     In addition to selecting differing line screen values for the hidden warning message and the background pattern to allow them to be used to prevent duplication, it is also known to use different respective tonal screen values (i.e., the percentage of ink coverage) can also be selected to differ so that the hidden warning message more easily appears on a reproduction of the original document. Known tonal screen values that are used to print these types of hidden warning messages and background patterns are, e.g., 12% and 10%, respectively (i.e., a tonal screen value ratio of about 1.2). 
     Because of the disparity between the respective line screen values and respective tonal screen values of the hidden warning message and background pattern, a mere combination of these two techniques would not be effective because the hidden warning message would normally be visible to a casual observer of the original. To minimize the visible appearance of the warning message with this combined technique, the respective tonal screen values are selected so that they are more similar and/or a camouflage pattern can be printed over the hidden warning message and background to obscure the hidden warning message from a casual observer of the original document. The camouflage pattern may be defined by areas in which dots, lines, bars, or marks have been formed for both the hidden warning message and background pattern, or the background pattern may be defined by a pattern of dots, lines, bars, or marks which are smaller than or larger than those used in the hidden warning message and background pattern, or by areas of complete coverage of a paler ink. 
     A description of these aforementioned techniques can be found in U.S. Pat. Nos. 4,227,720 and 5,197,795. 
     Another technique and example for creating duplication resistant documents is illustrated in U.S. Pat. Nos. 5,271,645, 5,018,767, and 5,193,853, whereby printed line frequencies are printed at specific angles that mis-register with the protocols of electronic color scanners causing a moire pattern when copied. 
     While the above techniques have provided some degree of protection of original documents with respect to most copiers, in recent years digital scanners and color copiers have improved substantially. These new color copiers, such as the Canon 700 and 800 series, have made the above techniques less effective in protecting original documents. By manipulating the control settings on such devices, copies can be made of such original documents in which the hidden warning message does not readily appear on reproductions when some of the most commonly used frequency and element size combinations are used. When the contrast setting of these modern photocopiers are set to the lighter settings or the copier is set to a built-in halftone setting, the resolution of the copier is such that it neither reproduces the lower line screen value/high tonal screen value hidden warning message nor the higher line screen value/lower tonal screen value background pattern. If the line screen value and tonal screen value of the hidden warning message is adjusted so that the lower line screen value/high tonal screen value hidden warning message is reproduced at a lighter copier setting, both the higher line screen value/lower tonal screen value background pattern and the lower line screen value/higher tonal screen value hidden warning message are reproduced. In both cases, the hidden warning message does not readily appear on the reproduction of the original document, so that a casual observer of the document may not be alerted that the document they have is not the original. 
     A greater disparity between the respective line screen values and tonal screen values of the hidden warning message and background pattern would allow the hidden warning message to appear on a reproduction of the original document even with the manipulation of the copier. Due to the great disparity, however, presently known camouflage techniques do not adequately suppress the visual appearance of the hidden warning message on the original document. This could result in the original document being rejected as a copy which is not acceptable to issuers of the original. 
     There thus remains a need to provide a counterfeit resistant and copy resistant original document and technique that effectively suppresses the visual appearance of a hidden warning message on the original document, while at the same time, effectively causing the hidden message to visibly appear on copies of the original, thereby precluding an unscrupulous copyist from suppressing the hidden warning message on a reproduction of the original document by manipulation of the control settings of the copying or scanning device. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a novel duplication resistant document and method of producing such a document that when reproduced exhibits a latent message. In a preferred method and embodiment of the present invention, a document comprises a substrate on which a message layer and a camouflaging layer are formed. The message layer comprises a latent message and a background. The contrast between the latent message and the background is such that the latent message is visible on a reproduction of the document. The dynamic camouflaging layer preferably comprises an environmentally varying ink; such as, thermochromic ink, that is formed onto the substrate as a camouflage pattern. The visual density of thermochromic ink inversely varies with temperature; such that, the appearance of the camouflaging layer is different at room temperatures and photocopying or scanning temperatures. 
     In alternative preferred embodiments, combinations of multi-tone contrasting layers, vignetted contrasting layers, multi-patterned dynamic camouflaging layers, and multi-spectral dynamic camouflaging layers are employed in accordance with the inventive features of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a depiction of an exploded view of a counterfeit-resistant document according to a preferred embodiment of the present invention. 
     FIG. 2 is a depiction of a top view of the contrasting layer of the counterfeit-resistant document of FIG.  1 . 
     FIG. 2 a  is an enlargement of the circled latent image of FIG.  2 . 
     FIGS. 3A to  3 E are latent messages that preferably employed with the contrasting layer of FIG.  1 . 
     FIGS. 4A to  4 G are camouflage patterns preferably employed with the dynamic camouflaging layer of the counterfeit-resistant document of FIG.  1 . 
     FIG. 5 is a depiction of a top view of the original counterfeit-resistant document of FIG.  1 . 
     FIG. 6 is a depiction of a top view of a reproduction of the counterfeit-resistant document of FIG. 5; 
     FIG. 7 is a depiction of a top view of a multi-tone counterfeit-resistant document according to an alternative preferred embodiment of the present invention; 
     FIG. 8 is a depiction of a top view of a multi-tone contrasting layer of the multi-tone counterfeit-resistant document of FIG. 7; 
     FIG. 9 is a depiction of a top view of a reproduction of the counterfeit-resistant document of FIG. 7 produced at a first copying device control setting; 
     FIG. 10 is a depiction of a top view of a reproduction of the counterfeit-resistant document of FIG. 7 produced at a second copying device control setting; 
     FIG. 11 is a depiction of a top view of a counterfeit-resistant document according to an alternative preferred embodiment of the present invention; 
     FIG. 12 is a depiction of a top view of a vignetted contrasting layer employed in the counterfeit-resistant document of FIG. 11; 
     FIG. 13 is a depiction of a top view of a reproduction of the counterfeit-resistant document of FIG. 11 produced at a first copying device control setting; 
     FIG. 14 is a depiction of a top view of a reproduction of the counterfeit-resistant document of FIG. 11 produced at a second copying device control setting; 
     FIG. 15 is a depiction of a top view of a counterfeit-resistant document exhibiting a multi-patterned dynamic camouflaging layer according to an alternative preferred embodiment of the present invention; 
     FIG. 16 is a depiction of a top view of a reproduction of the counterfeit-resistant document of FIG. 15; 
     FIG. 17 is a depiction of a top view of a counterfeit-resistant document exhibiting a discrete multi-spectral dynamic camouflaging layer according to an alternative preferred embodiment of the present invention; 
     FIG. 18 is a depiction of a top view of a reproduction of the counterfeit-resistant document of FIG. 17; 
     FIG. 19 is a depiction of a top view of a counterfeit-resistant document exhibiting a prismatic multi-spectral dynamic camouflaging layer according to an alternative preferred embodiment of the present invention. 
     FIG. 20 is a depiction of a top view of a reproduction of the counterfeit-resistant of FIG.  19 . 
     FIG. 21 is a depiction of a top view of a counterfeit-resistant document according to an alternative preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 depicts a counterfeit-resistant original document  10  (in this case, a stock certificate) comprising a substrate  12 , a contrasting layer  14  comprising a latent message  16  and a background  18 , and a dynamic camouflaging layer  20  comprising a camouflage pattern  22 . The substrate  12  is preferably of paper stock. Any material suitable for printing, however, may be used without departing from the scope of the present invention. As depicted, bearer information  11  is printed on the substrate  12 . The contrasting layer  14  is printed on the substrate  12  over the bearer information  11 , and the dynamic camouflaging layer  20  is printed over the contrasting layer  14 . 
     As shown in FIG. 2, the latent message  16  contrasts with the background  18  and visually appears to a casual observer in the absence of the dynamic camouflaging layer  20 . The latent message  16  comprises text, as shown in FIG. 2, but can alternatively comprise any indicia; such as, an image that conveys information to an observer of the original document  10 . The latent message  16  and background  18  are each printed as a halftone image. The latent message  16  comprises a pattern of elements with a relatively low line screen value and large element size. The background  18  comprises a pattern of elements with a relatively high line screen value and small element size. In the preferred embodiment, the elements are dots, but can alternatively comprise of lines or marks. The disparity between the contrast of the latent message  16  and the background  18  is, such that, the latent message  16  visually appears on the reproduction of the original document  10  over a wide range of copying device control settings. Respective line screen values for the latent message  16  and background of 50 LPI and 150 LPI (i.e., a line screen value ratio of 3), and respective tonal screen values for the latent message  16  and background  18  of 8% and 5% (i.e., a tonal screen value ratio of 1.6), result in the consistent visual appearance of the latent message  16  given the present state of the xerographical technology. 
     FIGS. 3A-3E, respectively, depict various examples of latent messages  16   a - 16   e  that can be formed in the contrasting layer  14 , preferably, to enhance the suppression of the latent message  16  on the original document  10 . The pattern of the latent message  16  is irregular, and the surface area covered by the latent message  16  is approximately equal to or greater than the surface area-covered by the background  18 . 
     The graphics pattern of the dynamic camouflaging layer  20  plays a significant role in camouflaging the latent message  16 . In general, the graphics pattern of the dynamic camouflaging layer  20  is preferably formed with a certain level of irregularity to its pattern to facilitate camouflaging of the latent message  16 . The more irregular patterns, with a greater diversity of tones or alternating solid/open areas, are the easiest to print and camouflage the latent message  16 , but lose some effectiveness when digitally copied. On the other hand, the smoother, more evenly spaced patterns, are more difficult to print without noticing the latent message  16 , but are more effective when digitally copied. 
     FIGS. 4A-4G respectively depict various examples of camouflage patterns  22   a - 22   g , that can be effectively employed with the dynamic camouflaging layer  20 . The camouflage pattern  22  can comprise words such as shown in the camouflage pattern  22   e  of FIG.  4 E. 
     The ratio of the area of the printed markings, to the total area on which the markings are printed, is preferably approximately 50% to provide a more similar visual appearance between the latent message  16  and the background  18 , thereby, aiding in the suppression of the latent image  16  to a casual observer of the original document  10 . 
     The ink density of the dynamic camouflaging layer  20  also plays a role in camouflaging the latent message  16 . Ink density or color is a sensory perception and can be perceived only in conjunction with light. The light penetrates into the transparent color of the ink film. When passing through the ink, the light continuously strikes against pigments, which, depending on the ink film thickness and the pigment concentration, absorb a greater or lesser part of certain wavelengths of light. When the light rays finally reach the printed substrate surface they are reflected back. After traveling back through the printed ink film, that proportion of the light which has not been absorbed by the ink, exits. It is this part of the light that is perceived by the eye of the observer and forms the assessment basis for color saturation. It is also this part of the light that is optically recognized by electronic devices. 
     There is a correlation between ink film thickness and ink density. The absorption behavior of an ink film depends on, the hue, the ink film thickness, and on the nature, as well as, the concentration of the printing ink pigmentation. Since, however, the color hue for process colors is standardized and the pigment concentration for these colors is also specified within a certain framework, only the ink film thickness remains as a variable which can be influenced. 
     The amount of light that is reflected from the surface of the printed substrate can be measured by a GreyTag D19C densitometer to quantify the density variations the eye perceives. Ink density values are expressed as logarithmic numbers. As the logarithmic density values increase, the amount of available light decreases. For example, a density of 0.00 indicates that 100% of incident light is reflected. A density of 1.00 indicates that only 10% of the incident light is reflected. A density of 2.00 indicates that only 1% of the incident light is reflected. This conversion is designed to adapt the density measurement to the peculiarities of the human sensory perception. 
     In general, as the density of the dynamic camouflaging layer  20  increases, the less the light incident on the contrasting layer  14  is reflected back through the dynamic camouflaging layer  20 , and the more the latent message  16  is suppressed with respect to the original document  10 . Suppression of the latent message  16  furthers the interest of not falsely alerting a casual observer of the original document  10  that it is otherwise. As the density of the dynamic camouflaging layer  20  decreases, the more the light incident on the contrasting layer  14  is reflected back through the dynamic camouflaging layer  20 , and the more the latent message  16  is exhibited. Exhibition of the latent message  16  furthers the interest of allowing a copying device to capture the latent message  16 , thereby creating a reproduction of the original document  16  on which the latent message  16  visually appears to a casual observer. In light of these countervailing interests, it is difficult, using standard inks, to both suppress a message situated in a highly contrastable pattern of an original document during normal viewing conditions and exhibit the message on a reproduction of the original document. Such is this case, with the latent message  16  found in the contrasting layer  14 . 
     The dynamic camouflaging layer  20  comprises an environmentally density changing ink, such as a thermochromic ink (i.e., an ink the color and density of which changes with temperature). The thermochromic ink is formulated with heat crystals, which renders the pigment portion of the ink subject to spectral changes when exposed to specific temperature levels. Thus, the thermochromic ink will undergo a visible change in density and color (i.e., hue and/or saturation) when exposed to the proper temperature range. The thermochromic ink, used to form the dynamic camouflaging layer  16 , darkens as the temperature decreases, and lightens as the temperature increases. In general, the darker the ink, the greater the visual density. Thus, the visual density of the thermochromic ink is inversely proportional to the temperature to which the ink is exposed. The composition and method of making thermochromic inks, and effects thereof, are disclosed in pending application Ser. No. 08/602,243, now U.S. Pat. No. 5,873,604, entitled “Document Security System Having Thermographic Pantograph and Validation Mark,” and filed by George K. Phillips on Feb. 16, 1996, which is fully incorporated herein by reference. 
     Because the visual density of the thermochromic ink is inversely proportional to temperature levels, the color of the dynamic camouflaging layer  20  darkens at or below room temperature, thus becoming more dense and facilitating the suppression of the latent message  16  on the original document  10  during normal viewing conditions; and lightens at temperatures to which typical copying devices subject a document (i.e., scanning temperatures), thus becoming less dense and facilitating the exhibition of the latent message  16  on a reproduction of the original document  10 . 
     The thermochromic ink has a dormant state when exposed to a low-level temperature range, and an activated state when exposed to a high-level temperature range. That is, the dynamic camouflaging layer  20  suppresses the contrasting layer  16  at room temperature, so that the latent image  16  does not visually appear to a casual observer of the original document  10  (shown in FIG.  5 ); and exhibits the contrasting layer  16  during scanning temperatures, so that the latent image  16  visually appears to a casual observer of a reproduction  10 ′ of the original document  10  (shown in FIG.  6 ). 
     Selection of the exact color, reactive properties and graphics of the dynamic camouflaging layer  20  is preferably coordinated with the selection of the contrasting properties of the contrasting layer  14 . As the disparity between the respective line screen values and respective tonal screen values of the latent message  14  and the background  16  increases, the need for graphic balancing complexity and visual density of the dynamic camouflaging layer  20  at room temperature increases. Conversely, as the disparity between the respective line screen values and respective tonal screen values of the latent message  14  and the background  16  decreases, the need for graphic balancing complexity and visual density of the dynamic camouflaging layer  20  at scanning temperatures decreases. 
     The particular thermochromic ink selected preferably has a visual density at room temperature that is high enough to effectively suppress the latent message  16  on the original document  10 ; and a visual density at scanning temperatures that is low enough to effectively exhibit the underlying latent message  16  on a reproduction of the original document  10 . If the latent message  16  and background  18 , respectively, have screen values of 50 LPI and 10% and 150 LPI and 5%, thermochromic inks having a cold visual density level (i.e., a visual density level measured at 60° F. or below) between 0.15 and 0.80, and a warm visual density level (i.e., a visual density level measured at 76° or above) between 0.02 and 0.22 measured with a GREYTAG D19C densitometer, are preferably employed. The presently most preferred thermochromic inks, however, are thermochromic inks that have a cold visual density level between 0.15 and 0.35 and a warm visual density level between 0.08 and 0.22. The exact composition of thermochromic ink is preferably modified to effect the exact visual density changing properties of the thermochromic ink. Ultimately, selection of a preferred thermochromic ink depends on the exact temperatures to which the ink will be exposed and the opaqueness and color hue pigmentation of the ink. 
     The particular arrangement of the dynamic camouflaging layer  20  is preferably varied to optimize the camouflaging of the latent message  16 . The patterns shown in FIGS. 4A-4G, to varying extents, suppress the latent message  16  when viewing the original document  10 ; while exhibiting the latent message  16  when viewing a reproduction of the original document  10  given the above-mentioned cold and warm visual density ranges. In alternative embodiments, the environmentally varying ink used to form the dynamic camouflaging layer  20  is a photochromic ink (i.e., an ink the color of which changes with the intensity of light). The visual density of the photochromic ink is inversely proportional with the intensity of light. Under a low-intensity light (e.g., ambient light found in a lit room), the visual density of the photochromic ink, like the thermochromic ink, is high enough that the latent image  14  on the original document  10  is suppressed. On the other hand, under a high-intensity light (e.g., light produced by a copier or scanner), the visual density of the photochromic ink, like the thermochromic ink, is low enough that the latent image  14  appears on the reproduction of the original document  10 . 
     FIG. 7 depicts an alternative preferred embodiment of a counterfeit-resistant original document  50  comprising a multi-tone contrasting layer  52  (see FIG.  8 ). To the extent the particular aspects of the original document  50  are the same as those of the original document  10 , the same reference numerals have been used. 
     As shown in FIG. 8, the multi-tone contrasting layer  52  has a first contrasting portion  54  and a second contrasting portion  56 . The first contrasting portion  54  comprises a first latent message  58  (faintly shown in FIG. 7) and a first background  60 . The elements of the first latent message  58  are larger than the elements of the first background  60 . Alternatively, however, the elements of the first latent message  58  are smaller than the elements of the first background  60 . The second contrasting portion  56  comprises a second latent message  62  (faintly shown in FIG. 7) and a second background  64 . The elements of the second latent message  62  are larger than the elements of the second background  64 . Alternatively, however, the elements of the second latent message  62  are smaller than the elements of the second background  64 . 
     The respective line screen values of the first latent message  58  and the second latent message  62  are different. Alternatively, however, the respective line screen values of the first latent message  58  and the second latent message  62  are the same. The respective line screen values of the first background  60  and the second background  64  are different. Alternatively, however, the respective line screen values of the first background  60  and the second background  64  are the same. 
     For instance, one useful combination is a line screen value of 50 LPI at 25% tonal screen value for the first latent message  58  and 150 LPI at 15% tonal screen value for the first background  60 ; and 50 LPI at 10% tonal screen value for the second latent message  62  and 150 LPI at 5% tonal screen value for the second background  64 . Another useful combination is a line screen value of 50 LPI at 25% tonal screen value for the first latent message  58  and 150 LPI at 15% tonal screen value for the first background  60 ; and 65 LPI at 12% tonal screen value for the second latent message  62  and 130 LPI at 5% tonal screen value for the second background  64 . Still another useful combination is a line screen value of 50 LPI at 10% tonal screen value for the first latent message  58  and 150 LPI at 50% tonal screen value for the first background  60 ; and 50 LPI at 15% tonal screen value for the second latent message  62  and 150 LPI at 5% tonal screen value for the second background  64 . 
     The first contrasting portion  54  has an overall tonal screen value that is more than that of the second contrasting portion  56 , and the first contrasting portion  54  appears darker than the second contrasting portion  56 . This enhances the difficulty of a copyist&#39;s manipulation of the control settings on the copying device in order to suppress the latent message on the reproduction of the original document  50 . That is, if the copying device is adjusted to obscure or eliminate the first latent message  58 , the second latent message  62  will appear on a reproduction  50 ′ of the original document  50 , as shown in FIG.  9 . Likewise, if the copying device is adjusted to obscure or eliminate the second latent message  62 , the first latent message  58  will appear on the reproduction  50 ′ of the original document  50 , as shown in FIG.  10 . 
     FIG. 11 depicts an alternative preferred embodiment of a counterfeit-resistant original document  80  comprising a vignetted contrasting layer  82  as shown in FIG.  12 . To the extent the particular aspects of the original document  80  are the same as those of the original document  10 , the same reference numerals have been used. 
     As depicted in FIG. 12, the vignetted contrasting layer  82  comprises a latent message  84  (shown faintly in FIG. 11) and a background  86 . The respective line screen values of the latent message  84  and the background  86  differ and are constant across the vignetted contrasting layer  82 . Preferably, the respective line screen values for the latent message  84  and background  86  are 50 LPI and 150 LPI. The size of the elements of the latent message  84  and background  86  differ and gradually vary across the vignetted contrasting layer  82 . That is, the tonal screen value of the vignetted contrasting layer  82  varies. Preferably, the respective tonal screen values of the latent message  84  and background  86  varies from 30% and 20% to 15% and 5% across the vignetted contrasting layer  82 . The tonal screen value of the illustrated vignetted contrasting layer  82  is preferably varied in steps, producing bands of slightly differing tone. In some applications, however, the tonal screen value of the vignetted contrasting layer  82  can continuously vary. The element size of the latent message  84  and the background  86  shown in FIG. 12 preferably vary horizontally across the original document  80 . The element size of the latent message  84  and the background  86  preferably vary in any direction (e.g., vertically or diagonally). 
     As with the multi-tone contrasting layer  52 , the additional feature provided by the vignetted contrasting layer  82  enhances the difficulty of the copyist in manipulation of the control settings on the copying device in an attempt to suppress the latent message on the reproduction of the original document  80 . That is, if the copying device is adjusted to obscure or eliminate the latent message  84 , at least a portion of the latent message  84  will appear on a reproduction  80 ′ of the original document  80  as shown in FIGS. 13 and 14, since the tonal screen value of the vignetted contrasting layer  82  varies. 
     In alternative embodiments, the element size of the latent message  84  varies across the across the vignetted contrasting layer  82 , while the element size of the background  86  remains uniform across the vignetted contrasting layer  82 ; or the element size of the background  86  varies across the vignetted contrasting layer  82 , while the element size of the latent message  84  remains uniform across the vignetted contrasting layer  82 . FIG. 15 depicts an alternative preferred embodiment of an original document  100  comprising a multi-patterned dynamic camouflaging layer  102 . To the extent the particular aspects of the original document  100  are the same as those of the original document  10 , the same reference numerals have been used. 
     The multi-patterned dynamic camouflaging layer  102  comprises multiple camouflage patterns, such as the camouflage patterns  22   e ,  22   a , and  22   b  depicted respectively in FIGS. 4E,  4 A, and  4 B. The multiple camouflage patterns are preferably selected to have differing suppression characteristics. As with the contrasting layers  52  and  82 , the multi-pattern dynamic camouflaging layer  102  enhances the difficulty of the copyist to manipulate the copying device control settings in an attempt to suppress the latent message  16  on the reproduction of the original document  100 . That is, because the multiple camouflage patterns provide differing suppression characteristics, it is more difficult to suppress the entire latent image  16  of the original document  100  as shown by a reproduction  100 ′ of the original document  100  in FIG.  16 . 
     FIG. 17 depicts an alternative preferred embodiment of an original document  120  comprising a discrete multi-spectral dynamic camouflaging layer  122 . To the extent the particular aspects of the original document  120  are the same as those of the original document  10 , the same reference numerals have been used. 
     The discrete multi-spectral dynamic camouflaging layer  122  comprises thermochromic ink that exhibits multiple colors and densities at any given temperature. The density of the thermochromic ink varies discretely over the discrete multi-spectral dynamic camouflaging layer  122  exhibiting discrete bands  124  of differing colors. 
     As with the multi-patterned dynamic camouflaging layer  102 , the discrete multi-spectral dynamic camouflaging layer  122  enhances the difficulty of the copyist in manipulating the copying device control settings in an attempt to suppress the latent message  16  on a reproduction  120 ′ of the original document  120 ′ as depicted in FIG.  18 . That is, because the multiple colored thermochromic ink densities provide differing suppression characteristics, it is more difficult to suppress the entire latent message  16  on the reproduction  120 ′ of the original document  120 . 
     FIG. 19 depicts an alternative preferred embodiment of an original document  140  comprising a prismatic multi-spectral dynamic camouflaging layer  142 . To the extent the particular aspects of the original document  140  are the same as those of the original document  10 , the same reference numerals have been used. The prismatic multi-spectral dynamic camouflaging layer  142  differs from the discrete multi-spectral dynamic camouflaging layer  122  in that the colors and density of the thermochromic ink varies continuously, rather than discretely over the prismatic multi-spectral dynamic camouflaging layer  142  exhibiting a prismatic effect. 
     As with the discrete multi-spectral dynamic camouflaging layer  122 , the prismatic multi-spectral dynamic camouflaging layer  142  enhances the difficulty of the copyist in manipulating the copying device control settings in an attempt to suppress the latent message  16  on a reproduction  140 ′ of the original document  140 ′ as depicted in FIG.  20 . 
     The preferred contrasting layers  14 ,  52  and  82 , and the preferred dynamic camouflaging layers  20 ,  102 ,  122 , and  142  can be combined in various ways to enhance the protection provided in further alternative preferred embodiments of the present invention. 
     In an alternative embodiment, the above-disclosed features can be incorporated into a document  160  having a thermochromic pantograph  162 , as depicted in FIG.  21 . The thermochromic pantograph  162  comprises a latent image  164 , which is concealed or obscured within the graphics of a camouflaged background pattern  166 . The latent image  164  layer of ink is preferably applied directly to substrate  168  while the thermochromic ink of the camouflage background pattern  166  is overprinted or trap produced within the latent image layer. 
     While embodiments and applications of this invention have been shown and described, it would be apparent, to the readers of this description, that many more modifications are possible without departing from the inventive concepts described herein. The invention, therefore, is not to be restricted beyond the scope and in the spirit of the appended claims.