Spatial integrating optical correlator for verifying the authenticity of a person, product or thing

• US 5,841,907 A
• Filed: 07/11/1997
• Issued: 11/24/1998
• Est. Priority Date: 11/14/1994
• Status: Expired due to Fees

• Current Assignee: University of Connecticut (State of Connecticut)
• Original Assignee: University of Connecticut (State of Connecticut)
• Inventors: Mok, Fai, Javidi, Bahram, Psaltis, Demetri
• Primary Examiner(s): Couso, Jose L.
• Assistant Examiner(s): Bella, Matthew C.
• Application Number:
  US08/890,380
• Time in Patent Office: 501 Days
• Field of Search: 382/278, 382/280, 382/210, 382/212, 382/218, 382/115, 359/29, 359/559, 359/560, 359/561, 372/26, 372/27
• US Class Current: 382/210
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence
• CPC Class Codes: G06V 10/895 the filter being related to phase processing, e.g. phase-only filters
• CPC Class Codes: G06V 40/1365 Matching; Classification
• CPC Class Codes: G07F 7/086 by passive credit-cards adapted therefor, e.g. constructive particularities to avoid counterfeiting, e.g. by inclusion of a physical or chemical security-layer for security documents G07D7/00; for the reading of record-carriers in general G06K7/00; for the design of coded credit-cards G06K19/10

Abstract

A method of verifying the authenticity of an object is disclosed employing a spatial integrating optical correlator. An unreadable and hence non-counterfeitable mask (e.g., a. complex mask or a phase mask) is coupled to the object and the optical correlator compares the mask with a reference mask on which it is scanned over. The correlator produces a correlation spot or image having an intensity which exceeds a given level if the mask is genuine. An alternate embodiment includes a fingerprint or other personalized pattern bonded to the mask, and the fingerprint or other personalized pattern on the card is compared to a reference fingerprint or other personalized pattern of the card holder for added security.

Claims

1. A method of verifying the authenticity of an object, the method comprising the steps of:

associating an input mask with the object. said input mask including a two dimensional function N(x,y);

scanning in one dimension said input mask with a light source to generate an input image;

projecting said input image at a reference mask in the spatial domain to generate a spatially integrated correlation image,

said reference mask includes a two dimensional function M_SDF (x,y) which includes possible shifts in the y-direction and is defined by, ##EQU5## where m₀ is the severity of misalignment in a y-direction for a system designed to detect a two dimensional function M(x,y) by one dimensional correlation, and

said correlation image has a function defined by,

space="preserve" listing-type="equation">R(x'"'"',y.sub.0)=∫

∫

N(x-x'"'"',y-y.sub.0)M.sub.SDF (x,y)dxdy;

detecting said correlation image to provide a correlation signal indicative of said correlation image; and

comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

2. The method of claim 1 wherein said step of detecting said correlation image comprises detecting the intensity of said correlation image.

3. The method of claim 1 wherein said step of associating said input mask with the object comprises affixing said input mask to the object.

4. The method of claim 1 wherein said object is a card.

5. The method of claim 1 further comprising the step of:

associating said reference mask with the object.

6. The method of claim 4 further comprising the steps of:

affixing said input mask the card; and

affixing said reference mask to the card.

7. The method of claim 1 wherein:

said input mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

8. The method of claim 1 wherein:

said input mask includes a phase pattern; and

said reference mask includes a phase pattern.

9. A method of verifying the authenticity of an object, the method comprising the steps of:

associating an input mask with the object, said input mask includes a two dimensional function N(x,y);

providing a spatial integrating optical correlator having an input plane and an output plane;

scanning in one dimension said input mask with a light source to generate an input image at said input plane of said correlator;

projecting said input image at a reference mask in the spatial domain to generate a spatially integrated correlation image at said output plane of said correlator,

said reference mask includes a two dimensional function M_SDF (x,y) which includes possible shifts in the y-direction and is defined by, ##EQU6## where m₀ is the severity of misalignment in a y-direction for a system designed to detect a two dimensional function M(x,y) by one dimensional correlation;

said correlation image has a function defined by,

space="preserve" listing-type="equation">R(x'"'"',y.sub.0)=∫

∫

N(x-x'"'"', y-y.sub.0)M.sub.SDF (x,y)dxdy;

detecting said correlation image to provide a correlation signal indicative of said correlation image; and

comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

10. The method of claim 9 wherein said step of detecting said correlation image comprises detecting the intensity of said correlation image.

11. The method of claim 9 wherein said step of associating said input mask with the object comprises:

affixing said input mask to the object.

12. The method of claim 9 wherein said object is a card.

13. The method of claim 9 further comprising the step of:

associating said reference mask with the object.

14. The method of claim 12 further comprising the steps of:

affixing said input mask the card; and

affixing said reference mask to the card.

15. The method of claim 9 wherein:

said input mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

16. The method of claim 9 wherein:

said input mask includes a phase pattern; and

said reference mask includes a phase pattern.

17. An apparatus for verifying the authenticity of an object having an input mask coupled thereto, comprising:

a partially coherent light source;

means for scanning in one dimension said input mask with said light source to generate an input image, said input mask includes a two dimensional function N(x,y);

a reference mask including a two dimensional function M_SDF (x,y) which includes possible shifts in the y-direction and is defined by, ##EQU7## where m₀ is the severity of misalignment in a y-direction for a system designed to detect a two dimensional function M(x,y) by one dimensional correlation;

means for projecting said input image at said reference mask in the spatial domain to generate a spatially integrated correlation image having a function defined by,

space="preserve" listing-type="equation">R(x'"'"',y.sub.0)=∫

∫

N(x-x'"'"',y-y.sub.0)M.sub.SDF (x,y)dxdy;

means for detecting said correlation image to provide a correlation signal indicative of said correlation image; and

means for comparing said correlation signal to a threshold level to verify to the authenticity of the object.

18. The apparatus of claim 17 wherein said means for detecting comprises means for detecting the intensity of said correlation image.

19. The apparatus of claim 17 wherein said object comprises a card having said input mask affixed thereto.

20. The apparatus of claim 17 wherein said object comprises a card having said input mask and said reference mask affixed thereto.

21. The apparatus of claim 17 wherein:

said input mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

22. The apparatus of claim 17 wherein:

said input mask includes a phase pattern; and

said reference mask includes a phase pattern.

23. An apparatus for verifying the authenticity of an object having an input mask coupled thereto, comprising:

a partially coherent light source;

a spatial integrating optical correlator having an input plane and an output plane;

means for scanning in one dimension said input mask with said light source to generate an input image at said input plane of said correlator, said input mask includes a two dimensional function N(x,y);

a reference mask including a two dimensional function M_SDF (x,y) which includes possible shifts in the v-direction and is defined by, ##EQU8## where m₀ is the severity of misalignment in a y-direction for a system designed to detect a two dimensional function M(x,y) by one dimensional correlation;

means for projecting said input image at said reference mask in the spatial domain to generate a spatially integrated correlation image at said output plane of said correlator, said correlation image has a function defined by,

space="preserve" listing-type="equation">R(x'"'"'y.sub.0)=∫

∫

N(x-x'"'"',y-y.sub.0)M.sub.SDF (x,y)dxdy;

means for detecting said correlation image to provide a correlation signal indicative of said correlation image; and

means for comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

24. The apparatus of claim 23 wherein said means for detecting comprises means for detecting the intensity of said correlation image.

25. The apparatus of claim 23 wherein said object comprises a card having said input mask affixed thereto.

26. The apparatus of claim 23 wherein said object comprises a card having said input mask and said reference mask affixed thereto.

27. The apparatus of claim 23 wherein:

said input mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

28. The apparatus of claim 23 wherein:

said input mask includes a phase pattern; and

said reference mask includes a phase pattern.

29. A method of verifying the authenticity of an object, the method comprising the steps of:

converting a biometric signature into a first mask including a one dimensional function f(x);

bonding a second mask to said first mask to form an input mask, wherein said input mask is a composite mask, said second mask including a one dimensional function M(x), said one dimensional function M(x) is defined by,

space="preserve" listing-type="equation">M(x)=e.sup.iφ

.sbsp.m.sup.(x)

where φ

m(x) is a random function, whereby said composite mask includes a one dimensional function g(x), said function g(x) being defined by,

space="preserve" listing-type="equation">g(x)=f(x)M(x);

associating said input mask with the object;

scanning in one dimension said input mask with a light source to generate an input image;

projecting said input image at a reference mask in the spatial domain to generate a spatially integrated correlation image, said reference mask including a one dimensional function M*(x), where * is the complex conjugate, and said correlation image has a function R(x) defined by,

space="preserve" listing-type="equation">R(x)=∫

M*(x-x'"'"')g(x)dx;

detecting said correlation image to provide a correlation signal indicative of said correlation image; and

comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

30. The method of claim 29 wherein said step of detecting said correlation image comprises detecting the intensity of said correlation image.

31. The method of claim 29 wherein said step of associating said input mask with the object comprises:

affixing said input mask to the object.

32. The method of claim 29 wherein said object is a card.

33. The method of claim 29 further comprising the step of:

associating said reference mask with the object.

34. The method of claim 32 further comprising the steps of:

affixing said input mask the card; and

affixing said reference mask to the card.

35. The method of claim 29 wherein said object is a card;

and the method further comprising the steps of;

affixing said composite mask the card; and

affixing said reference mask to the card.

36. The method of claim 29 wherein:

said first mask includes a complex phase/amplitude pattern;

said second mask includes a complex phase/amplitude pattern;

whereby said composite mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

37. The method of claim 29 wherein:

said first mask includes a phase pattern;

said second mask includes a phase pattern;

whereby said composite mask includes a phase pattern; and

said reference mask includes a phase pattern.

38. A method of verifying the authenticity of an object, the method comprising the steps of:

converting a biometric signature into a first mask including a one dimensional function f(x); and

bonding a second mask to said first mask to form an input mask, wherein said input mask is a composite mask, said second mask including a one dimensional function M(x), said one dimensional function M(x) is defined by,

space="preserve" listing-type="equation">M(x)=e .sup.iφ

.sbsp.m.sup.(x)

where φ

_m (x) is a random function, whereby said composite mask includes a one dimensional function g(x), said function g(x) being defined by,

space="preserve" listing-type="equation">g(x)=f(x)M(x);

associating an input mask with the object;

providing a spatial integrating optical correlator having an input plane and an output plane;

scanning in one dimension said input mask with a light source to generate an input image at said input plane of said correlator;

projecting said input image at a reference mask in the spatial domain to generate a spatially integrated correlation image at said output plane of said correlator, said reference mask includes a one dimensional function M*(x), where * is the complex conjugate, and said correlation image has a function R(x) defined by,

space="preserve" listing-type="equation">R(x)=∫

M*(x-x'"'"')g(x)dx;

detecting said correlation image to provide a correlation signal indicative of said correlation image; and

comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

39. The method of claim 38 wherein said step of detecting said correlation image comprises detecting the intensity of said correlation image.

40. The method of claim 38 wherein said step of associating said input mask with the object comprises:

affixing said input mask to the object.

41. The method of claim 38 wherein said object is a card.

42. The method of claim 38 further comprising the step of:

associating said reference mask with the object.

43. The method of claim 41 further comprising the steps of:

affixing said input mask the card; and

affixing said reference mask to the card.

44. The method of claim 38 wherein said object is a card;

and the method further comprising the steps of;

affixing said composite mask the card; and

affixing said reference mask to the card.

45. The method of claim 38 wherein;

said first mask includes a complex phase/amplitude pattern;

said second mask includes a complex phase/amplitude pattern;

whereby said composite mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

46. The method of claim 38 wherein:

said first mask includes a phase pattern;

said second mask includes a phase pattern;

whereby said composite mask includes a phase pattern; and

said reference mask includes a phase pattern.

47. An apparatus for verifying the authenticity of an object comprising:

a first mask including a biometric signature, said first mask including a one dimensional function f(x);

a second mask bonded to said first mask to form an input mask, wherein said input mask is a composite mask and is associated with the object, said second mask including a one dimensional function M(x), said one dimensional function M(x) is defined by,

space="preserve" listing-type="equation">M(x)=e.sup.iφ

.sbsp.m.sup.(x)

where φ

_m (x) is a random function, whereby said composite mask includes a one dimensional function g(x), said function g(x) being defined by,

space="preserve" listing-type="equation">g(x)=f(x)M(x);

a partially coherent light source;

means for scanning in one dimension said input mask with said light source to generate an input image;

a reference mask including a one dimensional function M*(x), where * is the complex conjugate;

means for projecting said input image at said reference mask in the spatial domain to generate a spatially integrated correlation image, said correlation image has a function R(x)defined by,

space="preserve" listing-type="equation">R(x)=∫

M*(x-x'"'"')g(x)dx;

means for detecting said correlation image to provide a correlation signal indicative of said correlation image; and

means for comparing said correlation signal to a threshold level to verify to the authenticity of the object.

48. The apparatus of claim 47 wherein said reference mask comprises a reference pattern stored in a thick optical material, the thickness of said optical material being at least several times the wavelength of light from which said reference pattern was written.

49. The apparatus of claim 47 wherein said means for detecting comprises means for detecting the intensity of said correlation image.

50. The apparatus of claim 47 wherein said object comprises a card having said input mask affixed thereto.

51. The apparatus of claim 47 wherein said object comprises a card having said input mask and said reference mask affixed thereto.

52. The apparatus of claim 47 wherein said object comprises a card having said composite mask and said reference mask affixed thereto.

53. The apparatus of claim 47 wherein:

said first mask includes a complex phase/amplitude pattern;

said second mask includes a complex phase/amplitude pattern;

whereby said composite mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

54. The apparatus of claim 47 wherein:

said first mask includes a phase pattern;

said second mask includes a phase pattern;

whereby said composite mask includes a phase pattern; and

said reference mask includes a phase pattern.

55. An apparatus for verifying the authenticity of an object comprising:

a first mask including a biometric signature, said first mask including a one dimensional function f(x);

a second mask bonded to said first mask to form said input mask, wherein said input mask is a composite mask and is associated with the object, said second mask includes a one dimensional function M(x), said one dimensional function M(x) is defined by,

space="preserve" listing-type="equation">M(x)=e.sup.iφ

.sbsp.m.sup.(X)

where φ

_m (x) is a random function, whereby said composite mask includes a one dimensional function g(x), said function g(x) being defined by,

space="preserve" listing-type="equation">g(x)=f(x)M(x);

a partially coherent light source;

a spatial integrating optical correlator having an input plane and an output plane;

means for scanning in one dimension said input mask with said light source to generate an input image at said input plane of said correlator;

a reference mask including a one dimensional function M*(x), where * is the complex conjugate;

means for projecting said input image at said reference mask in the spatial domain to generate a spatially integrated correlation image at said output plane of said correlator, said correlation image has a function R(x)defined by,

space="preserve" listing-type="equation">R(x)=∫

M*(x-x'"'"')g(x)dx;

means for detecting said correlation image to provide a correlation signal indicative of said correlation image; and

means for comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

56. The apparatus of claim 55 wherein said means for detecting comprises means for detecting the intensity of said correlation image.

57. The apparatus of claim 55 wherein said object comprises a card having said input mask affixed thereto.

58. The apparatus of claim 55 wherein said object comprises a card having said input mask and said reference mask affixed thereto.

59. The apparatus of claim 55 wherein said object comprises a card having said composite mask and said reference mask affixed thereto.

60. The apparatus of claim 55 wherein:

said first mask includes a complex phase/amplitude pattern;

said second mask includes a complex phase/amplitude pattern;

whereby said composite mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

61. The apparatus of claim 55 wherein:

said first mask includes a phase pattern;

said second mask includes a phase pattern;

whereby said composite mask includes a phase pattern; and

said reference mask includes a phase pattern.

62. A method of verifying the authenticity of an object, the method comprising the steps of:

converting a biometric signature into a first mask, said first mask includes a two dimensional function f(x,y);

bonding a second mask to said first mask to form an input mask, wherein said input mask is a composite mask, said second mask includes a two dimensional function M(x,y), said two dimensional function M(x,y) is defined by,

space="preserve" listing-type="equation">M(x,y)=e .sup.iφ

.sbsp.m.sup.(x,y)

where φ

_m (x,y) is a random function, whereby said composite mask includes a two dimensional function g(x,y), said function g(x,y) being defined by,

space="preserve" listing-type="equation">g(x,y)=f(x,y)M(x,y);

associating said input mask with the object;

scanning in one dimension said input mask with a light source to generate an input mask image;

projecting said input image at a reference mask in the spatial domain to generate a spatially integrated correlation image, said reference mask includes a two dimensional function M*(x,y), where * is the complex conjugate, and said correlation image has a function R(x,y) defined by,

space="preserve" listing-type="equation">R(x,y)=∫

∫

M*(x-x'"'"',y-y'"'"')g(x,y)dxdy;

detecting said correlation image to provide a correlation signal indicative of said correlation image; and

comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

63. The method of claim 62 wherein said step of detecting said correlation image comprises detecting the intensity of said correlation image.

64. The method of claim 62 wherein said step of associating said input mask with the object comprises:

affixing said input mask to the object.

65. The method of claim 62 wherein said object is a card.

66. The method of claims 62 further comprising the step of:

associating said reference mask with the object.

67. The method of claim 65 further comprising the steps of:

affixing said input mask the card; and

affixing said reference mask to the card.

68. The method of claim 62 wherein said object is a card;

and the method further comprising the steps of;

affixing said composite mask the card; and

affixing said reference mask to the card.

69. The method of claim 62 wherein:

said first mask includes a complex phase/amplitude pattern;

said second mask includes a complex phase/amplitude pattern;

whereby said composite mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

70. The method of claim 62 wherein:

said first mask includes a phase pattern;

said second mask includes a phase pattern;

whereby said composite mask includes a phase pattern; and

said reference mask includes a phase pattern.

71. A method of verifying the authenticity of an object, the method comprising the steps of:

converting a biometric signature into a first mask, said first mask including a two dimensional function f(x,y);

bonding a second mask to said first mask to form input mask, wherein said input mask is a composite mask, said second mask includes a two dimensional function M(x,y), said two dimensional function M(x,y) is defined by,

space="preserve" listing-type="equation">M(x,y)=e.sup.iφ

.sbsp.m.sup.(x,y)

where φ

_m (x,y) is a random function, whereby said composite mask includes a two dimensional function g(x,y), said function g(x,y) being defined by,

space="preserve" listing-type="equation">g(x,y)=f(x,y)M(x,y);

associating an input mask with the object;

providing a spatial integrating optical correlator having an input plane and an output plane;

scanning in one dimension said input mask with a light source to generate an input image at said input plane of said correlator,

projecting said input image at a reference mask in the spatial domain to generate a spatially integrated correlation image at said output plane of said correlator, said reference mask includes a two dimensional function M*(x,y), where * is the complex conjugate, and said correlation image has a function R(x,y) defined by,

space="preserve" listing-type="equation">R(x,y)=∫

∫

M*(x-x'"'"',y-y'"'"')g(x,y)dxdy;

detecting said correlation image to provide a correlation signal indicative of said correlation image; and

comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

72. The method of claim 71 wherein said step of detecting said correlation image comprises detecting the intensity of said correlation image.

73. The method of claim 71 wherein said step of associating said input mask with the object comprises:

affixing said input mask to the object.

74. The method of claim 71 wherein said object is a card.

75. The method of claim 71 further comprising the step of:

associating said reference mask with the object.

76. The method of claim 74 further comprising the steps of:

affixing said input mask the card; and

affixing said reference mask to the card.

77. The method of claim 71 wherein said object is a card;

and the method further comprising the steps of;

affixing said composite mask to the card; and

affixing said reference mask to the card.

78. The method of claim 71 wherein:

said first mask includes a complex phase/amplitude pattern;

said second mask includes a complex phase/amplitude pattern;

whereby said composite mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

79. The method of claim 71 wherein:

said first mask includes a phase pattern;

said second mask includes a phase pattern;

whereby said composite mask includes phase pattern; and

said reference mask includes a phase pattern.

80. An apparatus for verifying the authenticity of an object comprising:

a first mask including a biometric signature, said first mask includes a two dimensional function f(x,y);

a second mask bonded to said first mask to form an input mask, wherein said input mask is a composite mask and is associated with the object, said second mask includes a two dimensional function M(x,y), said two dimensional function M(x,y) is defined by,

space="preserve" listing-type="equation">M(x,y)=e.sup.iφ

.sbsp.m.sup.(x,y)

where φ

_m (x,y) is a random function, whereby said composite mask includes a two dimensional function g(x,y), said function g(x,y) being defined by,

space="preserve" listing-type="equation">g(x,y)=f(x,y)M(x,y);

a partially coherent light source;

means for scanning in one dimension said input mask with said light source to generate an input image;

a reference mask including a two dimensional function M*(x,y) where * is the complex conjugate;

means for projecting said input image at said reference mask in the spatial domain to generate a spatially integrated correlation image, said correlation image has a function R(x,y) defined by,

space="preserve" listing-type="equation">R(x,y)=∫

∫

M*(x-x'"'"',y-y'"'"')g(x,y)dxdy;

means for detecting said correlation image to provide a correlation signal indicative of said correlation image; and

means for comparing said correlation signal to a threshold level to verify to the authenticity of the object.

81. The apparatus of claim 80 wherein said reference mask comprises a reference pattern stored in a thick optical material, the thickness of said optical material being at least several times the wavelength of light from which said reference pattern was written.

82. The apparatus of claim 80 wherein said object comprises a card having said input mask affixed thereto.

83. The apparatus of claim 80 wherein said object comprises a card having said input mask and said reference mask affixed thereto.

84. The apparatus of claim 80 wherein said object comprises a card having said composite mask and said reference mask affixed thereto.

85. The apparatus of claim 80 wherein:

said first mask includes a complex phase/amplitude pattern;

said second mask includes a complex phase/amplitude pattern;

whereby said composite mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

86. The apparatus of claim 80 wherein:

said first mask includes a phase pattern;

said second mask includes a phase pattern;

whereby said composite mask includes a phase pattern; and

said reference mask includes a phase pattern.

87. An apparatus for verifying the authenticity of an object comprising:

a first mask including a biometric signature, said first mask including a two dimensional function f(x,y);

a second mask bonded to said first mask to form an input mask, wherein said input mask is a composite mask and is associated with the object, said second mask includes a two dimensional function M(x,y), said two dimensional function M(x,y) is defined by,

space="preserve" listing-type="equation">M(x,y)=e.sup.iφ

.sbsp.m.sup.(x,y)

where φ

_m (x,y) is a random function, whereby said composite mask includes a two dimensional function g(x,y), said function g(x,y) being defined by,

space="preserve" listing-type="equation">g(x,y)=f(x,y)M(x,y);

a partially coherent light source;

a spatial integrating optical correlator having an input plane and an output plane;

means for scanning in one dimension said input mask with said light source to generate an input image at said input plane of said correlator;

a reference mask including a two dimensional function M*(x,y), where * is the complex conjugate,

means for projecting said input image at said reference mask in the spatial domain to generate a spatially integrated correlation image at said output plane of said correlator, said correlation image has a function R(x,y) defined by,

space="preserve" listing-type="equation">R(x,y)=∫

∫

M*(x-x'"'"',y-y'"'"')g(x,y)dxdy;

means for detecting said correlation image to provide a correlation signal indicative of said correlation image; and

means for comparing said correlation signal to at least one threshold level to verify to the authenticity of the object.

88. The apparatus of claim 87 wherein said means for detecting comprises means for detecting the intensity of said correlation image.

89. The apparatus of claim 87 wherein said object comprises a card having said input mask affixed thereto.

90. The apparatus of claim 87 wherein said object comprises a card having said input mask and said reference mask affixed thereto.

91. The apparatus of claim 87 wherein said object comprises a card having said composite mask and said reference mask affixed thereto.

92. The apparatus of claim 87 wherein:

said first mask includes a complex phase/amplitude pattern;

said second mask includes a complex phase/amplitude pattern;

whereby said composite mask includes a complex phase/amplitude pattern; and

said reference mask includes a complex phase/amplitude pattern.

93. The apparatus of claim 87 wherein:

said first mask includes a phase pattern;

said second mask includes a phase pattern;

whereby said composite mask includes a phase pattern; and

said reference mask includes a phase pattern.