Cryptography – By modifying optical image
Reexamination Certificate
1998-10-26
2001-10-09
Swann, Tod (Department: 2132)
Cryptography
By modifying optical image
Reexamination Certificate
active
06301363
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to security documents including a security image composed of individual security image elements and complementary security image elements. When an attempt is made to duplicate or reproduce a document on which the security image is present, at least some of the security image elements change their appearance on the intended duplicate document, or are altered with respect to some other physical characteristic on the intended duplicate or reproduced document. The change in appearance, or the altered physical characteristic, of the elements is utilized to provide an indication that an attempt has been made to duplicate the document.
For example, the security image elements and the complementary security image elements are designed such that, upon the attempted duplication, e.g., by photocopying, either the security image elements or the complementary security image elements are altered while the others remain substantially the same. The elements are arranged such that the attempted duplication results in the formation of a readily apparent warning image on the face of the document. Specifically, when an attempt is made to copy the document, the word “VOID” may appear on the duplicate document. Further, the security image elements and the complementary security image elements are arranged such that the presence of the security image and the security image elements is not readily apparent on the original. Examples of security documents of this type are illustrated in U.S. Pat. Nos. 4,579,370, 5,149,140, 5,197,765, 5,340,159, the disclosures of which are incorporated herein by reference.
The above-described prior art provides a means by which a person charged with the responsibility of reviewing security documents can identify documents that are unauthorized copies of the original security document. However, despite the advantages of the conventional security documents there is a continuing demand in the security document industry for improved security documents and improved systems and methods for validating security documents.
BRIEF SUMMARY OF THE INVENTION
This continuing demand is met by the present invention wherein an improved system and method for viewing a subtle image on a security document and an improved security document including a subtle image are provided. The above reference to one type of conventional security document is not intended to limit the scope or application of the present invention to a specific type of security document. Rather, for the purposes of defining and describing the present invention, it should be understood that security image elements and complementary security image elements according to the present invention are any printed elements that function to provide an indication that an attempt has been made to duplicate or reproduce an original security document. The attempted duplication or reproduction could be through conventional or state of the art photocopying methods (analog, digital, color, black-and-white, etc.), printing methods (ink jet, laser, etc.), publishing methods, etc.
In accordance with one embodiment of the present invention, a system for viewing a subtle image on a security document is provided comprising a security document, a document viewer, and a document receiving station. The security document includes a subtle image formed on a first face of the document, wherein the subtle image is formed by a set of security image elements and a set of complementary security image elements, one of the set of security image elements and the set of complementary security image elements is not readily duplicated by a photocopier at a predetermined photocopier setting, while the other of the set of security image elements and the set of complementary security image elements is readily duplicated by the photocopier at the predetermined photocopier setting, the security image elements are arranged in a security image element array characterized by a first element array frequency f
1
, and the complementary security image elements are arranged in a complementary security image element array characterized by a second element array frequency f
2
. The document viewer comprises a plurality of lens elements arranged in a lens element array, wherein the plurality of lens elements define a document viewer focal plane, and the lens element array is characterized by a lens element array frequency f
0
, where f
0
, f
1
, and f
2
satisfy at least one of the following document characteristic equations
f
1
≡af
0
f
2
≡bf
0
f
0
≡cf
1
f
0
≡df
2
where a, b, c, and d are positive whole numbers and where a≢b and c≢d. The document receiving station is positioned to receive the document such that the document may be positioned substantially in the document viewer focal plane. The subtle image may comprise a repetitive array of warning terms.
Preferably, f
0
, f
1
, and f
2
satisfy at least two of the document characteristic equations. The lens element array frequency f
0
may be substantially equal to a selected one of the first element array frequency f
1
and the second element array frequency f
2
. Either the first element array frequency f
1
or the second element array frequency f
2
may be greater than the other of the first element array frequency f
1
and the second element array frequency f
2
. The lens element array frequency f
0
is preferably substantially equal to the lesser of the first element array frequency f
1
and the second element array frequency f
2
.
The document receiving station may be arranged to receive the document such that a selected one of the security image element array and the complementary security image element array is oriented along a first angle relative to the document receiving station and wherein the lens element array is oriented along the first angle. A selected one of the security image element array and the complementary security image element array may be oriented at a first angle relative to a longitudinal dimension of the document and the document receiving station may be positioned to receive the document such that the lens element array is oriented along the first angle relative to the longitudinal dimension of the document. The lens element array frequency f
0
may be substantially equal to the element array frequency of the selected element array.
The security image element array and the complementary security image element array may be oriented at different angles relative to a longitudinal dimension of the document. The lens element array may comprise a succession of lens elements spaced adjacent one another at the lens element array frequency f
0
. Respective ones of the lens elements may have a longitudinal dimension and a partially convex cross section perpendicular to the longitudinal dimension, wherein the cross section is substantially uniform along the longitudinal dimension.
In accordance with another embodiment of the present invention, a method of viewing a subtle image on a security document is provided comprising the steps of: identifying a security document comprising a subtle image formed on a first face of the security document, wherein the subtle image is formed by a set of security image elements and a set of complementary security image elements, one of the set of security image elements and the set of complementary security image elements is not readily duplicated by a photocopier at a predetermined photocopier setting, while the other of the set of security image elements and the set of complementary security image elements is readily duplicated by the photocopier at the predetermined photocopier setting, the security image elements are arranged in a security image element array characterized by a first element array frequency f
1
, and the complementary security image elements are arranged in a complementary security image element array characterized by a second element array frequency f
2
; providing a document viewer comprising a plurality of lens elements arranged in a lens element array
Killworth, Gottman Hagan & Schaeff, L.L.P.
Smithers Matthew
Swann Tod
The Standard Register Company
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