System and method for decoding digital encoded images

• US 20050237577A1
• Filed: 02/28/2005
• Published: 10/27/2005
• Est. Priority Date: 04/26/2004
• Status: Active Grant

• Current Assignee: Graphic Security Systems Corporation
• Original Assignee: Graphic Security Systems Corporation
• Inventors: Alasia, Alfred V., Alasia, Alfred J., Alasia, Thomas C., Cvetkovic, Slobodan
• Granted Patent: US 7,512,249 B2
• Time in Patent Office: Days
• US Class Current: 358/3.280
• CPC Class Codes: B42D 25/351 Translucent or partly translucent parts, e.g. windows
• CPC Class Codes: G06T 1/005 Robust watermarking, e.g. average attack or collusion attack resistant
• CPC Class Codes: G06T 2201/0051 Embedding of the watermark in the spatial domain
• CPC Class Codes: G06T 2201/0065 Extraction of an embedded watermark; Reliable detection
• CPC Class Codes: G06T 2201/0083 whereby only watermarked image required at decoder, e.g. source-based, blind, oblivious

Abstract

A method is presented for decoding an encoded image produced from a primary image and at least one secondary image using at least one encoding parameter. The encoded image is formed so that when the encoded image is printed, the secondary image is not discernible to a viewer without an optical decoding device having characteristics corresponding to the at least one encoding parameter. The method comprises obtaining a digital version of the encoded image, determining the at least one encoding parameter, and constructing a decoded image from the digital encoded image using at least one of the encoding parameters in the encoding parameter set.

Claims

1. A method for decoding an encoded image produced from a primary image and at least one secondary image using at least one encoding parameter, the encoded image being formed so that when the encoded image is printed, the secondary image is not discernible to a viewer without an optical decoding device having characteristics corresponding to the at least one encoding parameter, the method comprising:

obtaining a digital version of the encoded image;

determining the at least one encoding parameter; and

constructing a decoded image from the digital encoded image using the at least one encoding parameter.

2. A method for decoding an encoded image according to claim 1 wherein the action of constructing a decoded image includes:

rasterizing a control image to produce a rasterized control image having a rasterization frequency and orientation derived from the at least one encoding parameter;

comparing each pixel of the encoded image to a corresponding pixel in the rasterized control image to identify those encoded image pixels whose content is different from the content of the corresponding rasterized control image pixel;

constructing a difference image using the encoded image pixels whose content is different from the content of the corresponding rasterized control image pixel; and

forming the decoded image from the difference image.

3. A method for decoding an encoded image according to claim 2 wherein the control image is a blank image.

4. A method for decoding an encoded image according to claim 2 wherein the control image is a digital version of the primary image.

5. A method for decoding an encoded image according to claim 1 wherein the action of constructing a decoded image includes:

obtaining a first set of regular periodic samples of the encoded image, the configuration, orientation and frequency of these samples being derived from the at least one encoding parameter;

constructing a first composite sample image from the first set of regular periodic samples; and

expanding the samples of the first set of regular periodic samples to fill in spaces between the samples and form a first decoded image.

6. A method for decoding an encoded image according to claim 5 wherein each regular periodic sample is an elongate rectangular segment having a longitudinal centerline axis and wherein the frequency of the samples corresponds to an encoding frequency used to encode the encoded image and the angular orientation of the longitudinal centerline axis corresponds to an encoding angle used to encode the encoded image.

7. A method for decoding an encoded image according to claim 5 wherein the action of constructing a decoded image further includes:

obtaining a second set of regular periodic samples of the encoded image, the configuration, orientation and frequency of these samples being the same as for the first set of regular periodic samples except that the second set of regular periodic samples is offset from the first set of regular periodic samples by a predetermined fraction of the period between samples;

constructing a second composite sample image from the regular periodic samples; and

expanding the samples of the second set of regular periodic samples to fill in spaces between the samples and form a second decoded image.

8. A method for decoding an encoded image according to claim 7 wherein the action of constructing a decoded image further includes:

forming the decoded image by applying a layer flattening operation to the first and second decoded images.

9. A method for decoding an encoded image according to claim 8 wherein the layer-flattening operation includes conducting at least one of the actions consisting of dissolving, multiplying, averaging, overlaying, differencing and exclusion on the first and second decoded images.

10. A method for decoding an encoded image according to claim 1 further comprising:

enhancing the quality of the encoded image using one or more of the set consisting of median filtering, low-pass filtering, adaptive image filtering and morphological processing.

11. A method for decoding an encoded image according to claim 1 wherein the action of obtaining a digital version of the encoded image includes:

retrieving the digital version of the encoded image from data storage.

12. A method for decoding an encoded image according to claim 1 wherein the action of obtaining a digital version of the encoded image includes:

receiving the digital version of the encoded image from an encoding processor.

13. A method for decoding an encoded image according to claim 1 wherein the action of obtaining a digital version of the encoded image includes:

using image acquisition device to capture the digital version of the encoded image from a previously printed version of the encoded image.

14. A method for decoding an encoded image according to claim 13 wherein the image acquisition device is one of the set consisting of an optical scanner, a digital camera, and a system including an analog camera and a frame grabber.

15. A method for decoding an encoded image according to claim 1 wherein the action of determining the at least one encoding parameter includes:

retrieving the at least one encoding parameter from data storage.

16. A method for decoding an encoded image according to claim 1 wherein the action of determining the at least one encoding parameter includes:

receiving the at least one encoding parameter from an encoding processor.

17. A method of authenticating a digital document in which an encoded image has been embedded, the encoded image having been constructed using a plurality of encoding parameters and authentication content extracted from the digital document, the method comprising:

extracting the encoded image from the digital document;

digitally decoding the encoded image to produce a decoded image using the encoding parameters;

extracting decoded image content from the decoded image; and

comparing the decoded image information to the extracted authentication content.

18. A method according to claim 17 wherein the authentication content comprises an authentication image.

19. A method according to claim 17 wherein the authentication content comprises document specific data that are substantially unique to the digital document.

20. A method according to claim 17 wherein the action of comparing the decoded image content to the extracted authentication content includes:

determining whether the extracted decoded image content matches the authentication content.

21. A method according to claim 17 wherein the authentication content has been stored in a database and the action of comparing the decoded image content to the extracted authentication content includes:

retrieving the authentication content from the database.

22. A method according to claim 17 wherein the action of comparing the decoded image content to the extracted authentication content includes:

extracting the authentication content from the digital document.

23. A system for authenticating digital documents comprising:

an encoding module adapted for constructing an encoded image for embedding into a digital document, the encoded image being constructed using at least one encoding parameter and authentication content extracted from the digital document;

an embedding module in communication with the encoding module, the embedding module being adapted for embedding the encoded image into the digital document;

an encoding information database in selective communication with the encoding module, the database being adapted for storage of the at least one encoding parameter;

a decoding module in selective communication with the encoding information database, the decoding module being adapted for

receiving the digital document,

retrieving the at least one encoding parameter from the database,

extracting the encoded image from the digital document,

digitally decoding the encoded image to produce a decoded image using the at least one encoding parameter, and

extracting decoded image content from the decoded image;

an authentication module in communication with the decoding module, the authentication module being adapted for comparing the decoded image information to the extracted authentication content.

24. A system according to claim 23 wherein the system comprises a user data processor comprising an encoder interface module in selective communication with the encoding module and adapted for requesting an encoded image for embedding into the digital document.

25. A system according to claim 24 wherein one or more of the group consisting of the encoding module, embedding module, and encoding information database is part of the user data processor.

26. A system according to claim 23 wherein the system comprises an authentication server in selective communication with at least one user data processor over a network, wherein the decoding module and the authentication module are part of the authentication server, and wherein the authentication server is adapted for receiving a document authentication request from the at least one user data processor and for returning an authentication result to the at least one user data processor.

27. A method of enhancing the protection of a digital document in which a first encoded image has been embedded, the first encoded image having been constructed using a set of authentication content and a first encoding parameter set, the method comprising:

digitally decoding the first encoded image using the first encoding parameter set to produce a decoded image;

extracting the set of authentication content from the decoded image; and

constructing a second encoded image using the set of authentication content and a second encoding parameter set.

28. A method according to claim 27 wherein the authentication content comprises data that are substantially unique to the digital document.

29. A method according to claim 27 further comprising:

extracting the first encoded image from the digital document.

30. A method according to claim 27 further comprising:

embedding the second encoded image into the digital document.

31. A method according to claim 28 further comprising:

printing the digital document with the second encoded image embedded therein.

32. A method according to claim 31 further comprising:

receiving an authenticable document for authentication, the authenticable document having an authenticable encoded image embedded therein; and

authenticating the authenticable document by attempting to decode the authenticable encoded image using the second encoding parameter set.