Watermarking of digital object

• US 6,611,599 B2
• Filed: 09/29/1997
• Issued: 08/26/2003
• Est. Priority Date: 09/29/1997
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Natarajan, Balas K.
• Primary Examiner(s): Barron, Gilberto
• Assistant Examiner(s): Callahan, Paul E.
• Application Number:
  US08/939,215
• Publication Number:
  US 20020016916A1
• Time in Patent Office: 2,157 Days
• Field of Search: 382/232, 382/100, 380/5, 380/201, 380/203, 380/54, 380/55, 713/176
• US Class Current: 380/203
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: H04N 1/32144 embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
• CPC Class Codes: H04N 1/32208 involving changing the magnitude of selected pixels, e.g. overlay of information or super-imposition H04N1/32219, H04N1/32224 take precedence
• CPC Class Codes: H04N 1/32251 in multilevel data, e.g. greyscale or continuous tone data
• CPC Class Codes: H04N 1/32283 Hashing
• CPC Class Codes: H04N 2201/3233 of authentication information, e.g. digital signature, watermark
• CPC Class Codes: H04N 2201/3236 Details of authentication information generation
• CPC Class Codes: H04N 2201/327 which are undetectable to the naked eye, e.g. embedded codes

Abstract

A technique for identifying digital object using a digital watermark. The technique includes the steps of encrypting a message derived from source data on the digital object, to obtain an encrypted message digest (S); deriving a watermark from the encrypted message digest (S); and incorporating the watermark into the source data. The encryption is preferably done with a public key encryption system. The message to be encrypted can be obtained via performing a hash function on the source data on the digital object to obtain a message digest (M). The message digest (M) is the message encrypted with the signature encryption key to obtain the encrypted message digest (S). The watermark is resistant to cropping, scaling, and truncation.

Claims

1. A system for identifying a digital object using a digital watermark, comprising:

means for obtaining a set of source data from the digital object, the source data comprising a set of data values;

means for generating a message digest by applying a function to the source data which is preselected to avoid reconstruction of the source data from the message digest;

means for encrypting the message digest to obtain an encrypted message digest;

means for deriving a watermark vector from the encrypted message digest;

means for determining an average vector of a selected subset of the data values;

means for avoiding a dependency between the watermark vector and the average vector by orthogonalizing the watermark vector with respect to the average vector;

means for combining the watermark vector with the selected subset of the data values of the source data to obtain a watermarked object that includes the digital watermark.

2. The system of claim 1, wherein the function is preselected such that the message digest contains fewer bits than the source data.

3. The system of claim 1, wherein the means for deriving a watermark vector includes means for modulating the encrypted message digest to spread over a portion of a spectrum of the digital object.

4. The system of claim 1, wherein the means for encrypting the message digest comprises means for encrypting the message digest using a public key system.

5. An article of manufacture comprising a program storage medium, tangibly embodying a program code means readable by a computer to cause the computer to identify a digital object using a digital watermark, comprising:

code means for obtaining a set of source data from the digital object, the source data comprising a set of data values;

code means for generating a message digest by applying a function to the source data which is preselected to avoid reconstruction of the source data from the message digest;

code means for encrypting the message digest to obtain an encrypted message digest;

code means for deriving a watermark vector from the encrypted message digest;

code means for determining an average vector of a selected subset of the data values;

code means for avoiding a dependency between the watermark vector and the average vector by orthogonalizing the watermark vector with respect to the average vector;

code means for combining the watermark vector with the selected subset of the data values of the source data to obtain a watermarked object that includes the digital watermark.

6. The article of manufacture of claim 5, wherein the function is preselected such that the message digest contains fewer bits than the source data.

7. The article of manufacture of claim 5, wherein the code means for deriving a watermark vector includes code means for modulating the encrypted message digest to spread over a portion of a spectrum of the digital object.

8. The article of manufacture of claim 5, wherein the code means for encrypting the message digest comprises code means for encrypting the message digest using a public key system.

9. A method for identifying a digital object, comprising the steps of

deriving a watermark vector from the digital object;

determining an average vector of a selected subset of the digital object;

avoiding a dependency between the watermark vector and the average vector by orthogonalizing the watermark vector with respect to the average vector;

combining the watermark vector and the digital object.

10. The method of claim 9, wherein the step of deriving a watermark comprises the steps of:

generating a message digest by applying a function to the digital object which is preselected to avoid reconstruction of the digital object from the message digest;

encrypting the message digest to obtain an encrypted message digest;

deriving the watermark vector from the encrypted message digest.

11. The method of claim 9, further comprising the step of determining an average vector of a selected portion of the digital object.

12. The method of claim 11, A wherein the step of orthogonalizing comprises the step of orthogonalizing the watermark vector with respect to the average vector.

13. A method for identifying a digital object, comprising the steps of:

deriving a watermark vector from the digital object;

determining an average vector of a selected portion of the digital object;

avoiding a dependency between the watermark vector and the digital object by orthogonalizing the watermark vector with respect to the average vector;

combining the watermark vector with the digital object.

14. The method of claim 13, wherein the step of deriving a watermark comprises the steps of:

generating a message digest by applying a function to the digital object which is preselected to avoid reconstruction of the digital object from the message digest;

encrypting the message digest to obtain an encrypted message digest;

deriving the watermark vector from the encrypted message digest.