Authentication of documents and articles by moire patterns

• US 20040076310A1
• Filed: 10/16/2002
• Published: 04/22/2004
• Est. Priority Date: 10/16/2002
• Status: Active Grant

• Current Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Original Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Inventors: Hersch, Roger D., Chosson, Sylvain
• Granted Patent: US 7,194,105 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: B42D 25/342 Moiré effects
• CPC Class Codes: G07D 7/0032 using holograms
• CPC Class Codes: G07D 7/207 Matching patterns that are created by the interaction of two or more layers, e.g. moiré patterns

Abstract

The present invention relies on the moiré patterns generated when superposing a base layer made of base band patterns and a revealing line grating (revealing layer). The produced moiré patterns comprise an enlargement and a transformation of the individual patterns located within the base bands. Base bands and revealing line gratings may be rectilinear or curvilinear. When translating or rotating the revealing line grating on top of the base layer, the produced moiré patterns evolve smoothly, i.e. they may be smoothly shifted, sheared, and possibly be subject to further transformations. Base band patterns may incorporate any combination of shapes, intensities and colors, such as letter, digits, text, symbols, ornaments, logos, country emblems, etc. . . . . They therefore offer great possibilities for creating security documents and valuable articles taking advantage of the higher imaging capabilities of original imaging and printing systems, compared with the possibilities of the reproduction systems available to potential counterfeiters. Since the revealing line grating reflects a relatively high percentage of the incident light, the moiré patterns are easily apparent in reflective mode and under normal illumination conditions. They may be used for the authentication of any kinds of documents (banknotes, identity documents, checks, diploma, travel documents, tickets) and valuable articles (optical disks, CDs, DVDs, CD-ROMs, packages for medical drugs, bottles, articles with affixed labels).

Claims

1. A method for authenticating documents by using moiré

patterns, the method comprising the steps of;

a) superposing a document with a base layer comprising patterns and a revealing layer comprising a revealing line grating, thereby producing moiré

patterns and

b) comparing said moiré

patterns with reference moiré

patterns and depending on the result of the comparison, accepting or rejecting the document,

where successive lines of the revealing line grating sample within the base layer different instances of the patterns and where the produced moiré

patterns are a transformation of base layer patterns, said transformation comprising at least an enlargement.

2. The method of claim 1, where the base layer comprises at least one set of base bands and where base bands comprise patterns selected from the set of typographic characters, variable shape patterns, variable intensity patterns and variable color patterns.

3. The method of claim 2, where the patterns residing within successive base bands are similar.

4. The method of claim 2, where at least one set of base bands is curvilinear.

5. The method of claim 2, where the revealing line grating is curvilinear.

6. The method of claim 2, where base bands and the revealing line grating are curvilinear and where said curvilinear base bands and said curvilinear line grating are obtained by geometric transformations.

7. The method of claim 2, where documents are individualized according to the geometric transformation parameters used for generating the base layer and for generating its corresponding revealing layer.

8. The method of claim 6, where the base layer comprises multiple sets of base bands characterized by different parameters selected from the group of orientation parameters, period parameters, geometric transformation parameters and the parameters specifying the relative orientation and position of the base and revealing layers.

9. The method of claim 1, where the revealing line grating comprises lines selected from the group of continuous lines, dotted lines, interrupted lines and partially perforated lines.

10. The method of claim 1 where the base layer comprises multiple interlaced patterns and where shifting the revealing layer on top of the base layer produces moiré

patterns which comprise transformed and blended instances of the multiple interlaced patterns.

11. The method of claim 1, where the reference moiré

patterns are memorized reference moiré

patterns seen previously in a superposition of a base layer and a revealing layer in documents that are known to be authentic.

12. The method of claim 1, where the reference moiré

patterns are obtained according to a technique selected from the techniques of (a) image acquisition of the superposition of the base layer and the revealing layer, (b) computation of the superposition of base layer and revealing layer within a bytemap and (c) computation by applying a transformation to the base layer patterns.

13. The method of claim 1, where comparing the moiré

patterns with reference moiré

patterns is done by visualization.

14. The method of claim 1, where the base layer is imaged on an opaque support and the revealing layer on a transparent support.

15. The method of claim 1, where the base layer and the revealing layer are located on two different areas of the same document, thereby enabling the visualization of the moiré

pattern to be performed by superposition of the base layer and of the revealing layer of said document.

16. The method of claim 1, where the base layer is created by a process for transferring an image onto a support, said process being selected from the set comprising lithographic, photolithographic, photographic, electrophotographic, engraving, etching, perforating, embossing, ink jet and dye sublimation processes.

17. The method of claim 1, where the revealing layer is an element selected from the group comprising an opaque plastic with transparent lines, cylindric microlenses and a diffractive device emulating the behavior of cylindric microlenses.

18. The method of claim 1, where the document is an element selected from the group of banknote, check, trust paper, identification card, passport, travel document, ticket, valuable article, valuable product, label affixed on a valuable product, package of a valuable product.

19. The method of claim 1, where the base layer includes patterns whose colors gradually vary according to their position, thereby generating in the layer superposition moiré

patterns which vary in their colors according to their position.

20. The method of claim 1, where the base layer includes includes patterns of gradually varying shapes and is incorporated within an image selected from the group of variable intensity dithered image and color dithered image.

21. The method of claim 1, where the base layer includes patterns which are made of typographic characters forming at least one word of text.

22. The method of claim 2, where the base layer comprises multiple sets of base bands characterized by different parameters selected from the group of orientation parameters and period parameters.

23. The method of claim 1 where the base layer patterns are printed using at least one nonstandard ink, thus making its faithful reproduction difficult using the standard cyan, magenta, yellow and black printing colors available in common photocopiers and desktop systems.

24. The method of claim 1, where base layer patterns are at least partially reproduced with a metallic ink, thereby creating at specular observation angles strongly visible moiré

patterns.

25. The method of claim 1 where comparing the moiré

patterns with reference moiré

patterns is done by comparing at least one element of the moiré

patterns with at least one element of the reference moiré

patterns.

26. The method of claim 1, where comparing the moiré

patterns with reference moiré

patterns consists in comparing a code incorporated into the moiré

patterns with a reference code located on the same document.

27. The method of claim 1, where comparing the moiré

patterns with reference moiré

patterns consists in decrypting a code incorporated into the moiré

patterns and comparing it with a reference decrypted code.

28. The method of claim 1, where the base layer comprises an image dithered with a dither matrix incorporating base band patterns, where without revealing layer the image appears and with the revealing layer moiré

patterns appear which allow to verify the authenticity of the document.

29. The method of claim 28, where the image is a photograph of the document holder.

30. A security document comprising

(a) a base layer comprising base bands, said base bands comprising patterns, and

(b) a revealing layer comprising a line grating,

where the superposition of the base bands and the revealing layer produces moiré

patterns, which are transformed instances of the base band patterns, the transformation comprising an enlargement.

31. The security document of claim 30, where individual base bands comprise patterns selected from the set of typographic characters, variable shape patterns, variable intensity patterns and variable color patterns.

32. The security document of claim 31, where the patterns residing within successive base bands are similar.

33. The security document of claim 30 where the base layer comprises multiple interlaced patterns and where shifting the revealing layer on top of the base layer produces moiré

patterns comprising transformed and blended instances of the multiple interlaced patterns.

34. The security document of claim 30, where at least one layer selected from the set of base band layer and revealing layer is curvilinear.

35. The security document of claim 34, where at least one curvilinear layer is obtained by a geometric transformation.

36. The security document of claim 30, where both the base band layer and the revealing layer are curvilinear and where documents are individualized according to the geometric transformation parameters selected for generating the base layer and for generating its corresponding revealing layer.

37. The security document of claim 35, where the base layer comprises multiple sets of base bands characterized by different parameters selected from the group of orientation parameters, period parameters, geometric transformation parameters and the parameters specifying the relative orientation and position of the base and revealing layers.

38. The security document of claim 30, where the revealing line grating comprises lines selected from the group of continuous lines, dotted lines, interrupted lines and partially perforated lines.

39. The method of claim 30 where the base layer comprises multiple interlaced patterns and where shifting the revealing layer on top of the base layer produces moiré

patterns which comprise transformed and blended instances of the multiple interlaced patterns.

40. The security document of claim 30, where the base layer is imaged on an opaque support and the revealing layer on a transparent support.

41. The security document of claim 30, where the base layer and the revealing layer are located on two different areas of the same document, thereby enabling the visualization of the moiré

pattern to be performed by superposition of the base layer and of the revealing layer of said document.

42. The security document of claim 30, where the base layer is created by a process for transferring an image onto a support, said process being selected from the set comprising lithographic, photolithographic, photographic, electrophotographic, engraving, etching, perforating, embossing, ink jet and dye sublimation processes.

43. The security document of claim 30, where the revealing layer comprises an element selected from the group comprising a film with transparent lines, an opaque plastic with transparent lines, cylindric microlenses and a diffractive device emulating the behavior of cylindric microlenses.

44. The security document of claim 30, where the document is an element selected from the group of banknote, check, trust paper, identification card, passport, travel document, ticket, valuable article, valuable product, label affixed on a valuable product, package of a valuable product.

45. The security document of claim 30, where at least one layer selected from the set comprising the base layer and the revealing layer is located on a valuable product, and where the other layer selected from the same set is located on the valuable product'"'"'s package.

46. The security document of claim 30, where the base layer comprises patterns whose colors gradually vary according to their position, thereby generating in the layer superposition moiré

patterns which vary in their colors according to their position.

47. The security document of claim 30, where the base layer comprises patterns of gradually varying shapes and is incorporated within an image selected from the group of variable intensity dithered image and color dithered image.

48. The security document of claim 30, where the base layer comprises patterns of variable intensity incorporated within a variable intensity image.

49. The security document of claim 30, where the base layer comprises patterns of variable color incorporated within a variable color image.

50. The security document of claim 30, where the base layer comprises an image dithered with a dither matrix comprising base band patterns, where without revealing layer the image appears and with the revealing layer moiré

patterns appear which allow to verify the authenticity of the document.

51. The security document of claim 50, where the image is a photograph of the document holder.

52. The security document of claim 50 where the dithered image comprises two levels of authentication:

the first level of authentication is embodied by a first level microstructure visible without superposing the revealing layer and the second level of authentication is embodied by second level moiré

patterns obtained by the superposition of the dithered image and of the revealing layer.

53. The security document of claim 30 where the base layer patterns are printed using at least one non-standard ink, thus making it difficult to faithfully reproduce said patterns using cyan, magenta, yellow and black printing colors available in standard color printers and photocopiers, thereby, when superposing base layer and revealing layer, making it very difficult to reproduce the original moiré

pattern.

54. The security document of claim 30, where comparing the moiré

patterns with reference moiré

patterns consists in comparing a code incorporated into the moiré

patterns with a reference code located on the same document.

55. The security document of claim 30, where the moiré

patterns incorporate a code enabling its authentication.

56. A security device for authenticating documents comprising

(a) a base layer comprising base bands, said base bands comprising patterns, and

(b) a revealing layer with a grating of lines,

where the superposition of the base bands and the revealing layer produces moiré

patterns, which are transformed instances of the base band patterns, the transformation comprising a least an enlargement and where the document authentication is done by the comparison of said moiré

patterns with reference moiré

patterns and the acceptance or the rejection of the document depending on the result of the comparison.

57. The security device of claim 56, where the base layer is embodied by an element selected from the set of transparent devices, opaque devices, optically variable devices and diffractive devices.

58. The security device of claim 56, where the revealing layer is embodied by an element selected from the group comprising an opaque plastic with transparent lines, cylindric microlenses and a diffractive device emulating the behavior of cylindric microlenses.

59. The security device of claim 56, where the base layer is a multichromatic base layer whose individual patterns are colored, thereby generating color moiré

patterns when the revealing layer is superposed on said base layer.

60. The security device of claim 56, where the base layer comprises patterns whose shapes gradually vary according to their position, thereby generating in the layer superposition moiré

patterns which vary in their shape according to their position.

61. The security device of claim 56, where the base layer includes comprises whose colors gradually vary according to their position, thereby generating in the layer superposition moiré

patterns which vary in their colors according to their position.

62. The security device of claim 56, where the base layer comprises patterns of gradually varying shapes and is incorporated within a variable intensity dithered image.

63. The security device of claim 56, where the base layer comprises patterns of gradually varying shapes and colors and is incorporated within a color dithered image.

64. The security device of claim 56, where the base layer comprises includes a pattern of variable intensity incorporated within a variable intensity image.

65. The security device of claim 56, where the base layer comprises includes a pattern of variable color incorporated within a variable color image.

66. The security device of claim 56, where at least one layer selected from the group of base band layer and revealing layer is curvilinear.

67. The security device of claim 66 where at least one curvilinear layer is obtained by a geometric transformation.

68. The security device of claim 67, where both the base band layer and the revealing layer are curvilinear and where documents are individualized according to the geometric transformation parameters selected for generating the base layer and for generating its corresponding revealing layer.

69. The method of claim 67, where the base layer comprises multiple sets of base bands characterized by different parameters selected from the group of orientation parameters, period parameters, geometric transformation parameters and the parameters specifying the relative orientation and position of the base and revealing layers.

70. The security device of claim 56 where the base layer comprises multiple interlaced patterns and where shifting the revealing layer on top of the base layer produces moiré

patterns which comprise transformed and blended instances of the multiple interlaced patterns.

71. The security device of claim 56, where comparing the moiré

patterns with reference moiré

patterns consists in comparing a code incorporated into the moiré

patterns with a reference code located on the same document.

72. The security device of claim 71, where comparing the moiré

patterns with reference moiré

patterns consists in decrypting a code incorporated into the moiré

patterns and comparing it with a reference decrypted code.

73. The security device of claim 56, where the base layer comprises an image dithered with a dither matrix incorporating base band patterns, where without revealing layer the image appears and with the revealing layer moiré

patterns appear which allow to verify the authenticity of the document.

74. The security device of claim 73, where the image is a photograph of the document holder.

75. The security device of claim 56, where the revealing line grating comprises lines selected from the group of continuous lines, dotted lines, interrupted lines and partially perforated lines.

76. The security device of claim 56 whose base layer is integrated into an item selected from the group of security documents, packages of valuable articles and valuable articles.

77. The security device of claim 56 whose base and revealing layers are integrated into an item selected from the group of security documents, packages of valuable articles and valuable articles.

78. The security device of claim 56, where at least one layer selected from the set comprising the base layer and the revealing layer is located on a valuable product, and where at least one other layer selected from the same set is located on the valuable product'"'"'s package.

79. The security device of claim 56 affixed to an item selected from the group of security documents, packages of valuable articles and valuable articles.

80. The security device of claim 78, where said valuable product is an optical disk.

81. An apparatus for authentication of documents making use of moiré

patterns, the apparatus comprising;

a) a revealing layer comprising a grating of lines;

b) an image acquisition means arranged to acquire moiré

patterns produced by the superposition of a base layer located on a document and the revealing layer; and

c) a comparing means operable for comparing the acquired moiré

patterns with reference moiré

patterns;

where successive lines of the revealing line grating sample within the base layer different instances of patterns, where the produced moiré

patterns are a transformation of base layer patterns, said transformation comprising at least an enlargement and where according to the comparison, the document is accepted or rejected.

82. The apparatus of claim 81, where at least one layer selected from the set comprising the base layer and the revealing layer is a curvilinear layer.

83. The apparatus of claim 81, where the curvilinear layer is a geometrically transformed layer.

84. The apparatus of claim 81 where the image acquisition means and comparing means are human biosystems, a human eye and brain respectively.

85. The apparatus of claim 81, where the comparing means is a comparing processor controlling a document handling device accepting, respectively rejecting a document to be authenticated, according to the comparison operated by the comparing processor.

86. The apparatus of claim 81, where the comparing processor is a microcomputer comprising a processor, memory and input-output ports and where the image acquisition means is a camera connected to said microcomputer.

87. The apparatus of claim 81 where the revealing layer with a grating of lines is an element selected from the group comprising an opaque plastic with transparent lines, cylindric microlenses and a diffractive device emulating the behavior of cylindric microlenses.

88. A computing system for the authentication of documents making use of moiré

patterns, the computing system comprising;

b) an interface to an image acquisition means arranged to acquire documents with a base layer comprising base bands, said base bands comprising patterns,

c) a program module multiplying in the computing system'"'"'s memory the acquired base layer with a corresponding revealing layer comprising a line grating yielding the digital image of the superposition of base layer and revealing layer;

d) a program module performing a low-pass filtering operation on the digital image of the superposition of base layer and revealing layer in order to compute the moiré

patterns;

c) a program module comparing the computed moiré

patterns with reference moiré

patterns, where the computed moiré

patterns are a transformation of base layer patterns, said transformation comprising at least an enlargement and where according to the comparison, the document is accepted or rejected.

89. The computing system of claim 88, where the revealing layer depends on the document to be authenticated.

90. The computing system of claim 89, which also comprises a module operable for identifying the document to be authenticated and determining which revealing layer needs to be applied in order to produce a superposition of base and revealing layer yielding the expected moiré

patterns.

91. The computing system of claim 88, where at least one layer selected from the set comprising the base layer and the revealing layer is a curvilinear layer.

92. The computing system of claim 88, where the image acquisition means is a camera connected to said computing system.