Method and apparatus for digital watermarking of images

• US 6,504,941 B2
• Filed: 04/30/1998
• Issued: 01/07/2003
• Est. Priority Date: 04/30/1998
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Wong, Ping Wah
• Primary Examiner(s): Johns, Andrew W.
• Assistant Examiner(s): NAKHJAVAN, SHERVIN K
• Application Number:
  US09/070,470
• Publication Number:
  US 20010046307A1
• Time in Patent Office: 1,713 Days
• Field of Search: 380/28, 380/54, 380/29, 380/30, 382/100, 382/232, 705/51
• US Class Current: 382/100
• CPC Class Codes: G06T 1/0035 Output size adaptive watermarking
• CPC Class Codes: G06T 2201/0061 Embedding of the watermark in each block of the image, e.g. segmented watermarking
• CPC Class Codes: H04N 1/32203 Spatial or amplitude domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/32213 Modulating the least significant bits of pixels
• CPC Class Codes: H04N 1/32283 Hashing
• 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

The present invention provides an invisible digital watermarking technique that can serve the two purposes of ownership verification and authentication, that can detect changes in pixel values as well as image size, and that may be used in public key or alternatively, secret key watermarking systems. The watermark insertion procedure computes a hash function and then combines the output of the hashed function of a modified image block, a key and various image parameters with a block of the watermark bitmap, resulting in a combined image block. As a final step to create a watermarked image block, the combined image block is inserted into the LSB of the modified image. The watermark extraction procedure takes the watermarked image block and creates two different image blocks: a first image,block with the LSB'"'"'s of the watermarked image block set to zero, and a second image block with the LSB'"'"'s of the watermarked image block extracted. The watermark extraction procedure uses the hash function to calculate a digest of values, resulting in a hashed output. The hashed output is combined with the second image block, preferably using an exclusive OR function. The result of the combined hashed output with the second image block is a block of the extracted watermark.

Claims

1. An electronic system for inserting a watermark into a digital image, comprising:

means for modifying at least one predetermined bit within an image block X_r to a predetermined value, wherein the modified image block is X_r;

means for calculating a digest of values using a cryptographic hash function, wherein a user key, an image width, an image height and the modified image block are inputs to the means for calculating a digest of values, wherein the output of the means for calculating a digest of values is a hashed output, wherein the means for modifying at least one predetermined bit of the image block is electrically coupled to the means for calculating a digest of values;

means for combining the hashed output with a watermark, wherein the means for combining uses a pixel by pixel exclusive OR logic operation, wherein the means for combining the hashed output with a watermark is electrically coupled to the output of the means for calculating a digest of values, wherein the output of the means for combining is a combined image block C_r; and

means for inserting a first image block into the modified image block X_r, wherein the means for inserting the first image block into the modified image block X_r, is electrically coupled to the means for modifying at least one predetermined it of the image block.

2. The electronic system recited in claim 1 wherein the first image block is the combined image block C_r.

3. The electronic system recited in claim 2 wherein the means for combining the hashed output with a watermark is electrically coupled to the means for inserting the first image block into the modified image block X_r.

4. The electronic system recited in claim 1 wherein the first image block is an encrypted image block W_r.

5. The electronic system recited in claim 4 further including an encryption means, wherein the encryption means is electrically coupled to both the means for combining the hashed output with a watermark and the means for inserting a first image block into the modified image block X_r.

6. The electronic system recited in claim 1 wherein the means for modifying at least a predetermined bit to a predetermined value modifies the at least one predetermined bit independently for each color plane of the image block.

7. An electronic system for inserting a watermark into a digital image, comprising:

means for modifying at least one predetermined bit within an image block X₁, to a predetermined value, wherein the modified image block is X_r;

means for calculating a digest of values using a cryptographic hash function, wherein a user key, an image width, an image height and the modified image block are inputs to the means for calculating a digest of values, wherein the means for calculating a digest of values is a hashed output, wherein the means for modifying at least one predetermined bit of the image block is electrically coupled to the means for calculating a digest of values wherein the means for modifying at least one predetermined bit modifies the LSB within the image block X_r;

means for combining the bashed output with a watermark, wherein the means for combining uses a pixel by pixel XOR logic block, wherein the means for combining the hashed output with a watermark is electrically coupled to the means for calculating a digest of values, wherein the output of the means for combining is a combined image block; and

means for inserting a first image block into the modified image block X_r, wherein the means for inserting the first image block into the modified image block X_r is electrically coupled to the means for modifying at least one predetermined bit of the image block.

8. An electronic system for extracting a watermark from a digital watermarked image comprising

means for modifying at least a predetermined bit within an image block of the watermarked image to a predetermined value;

means for extracting at least a predetermined from the watermarked image block;

means for calculating a digest of values using a cryptographic hash function, wherein a user key, an image width, an image height and the modified image block are inputs to the means for calculating a digest of values, wherein the output of the means for calculating a digest of values using a cryptographic hash function is a hashed output, wherein the means for modifying at least a predetermined bit of the watermarked image is electrically coupled to the mans for calculating a digest of values;

means for combining, wherein the means for combining is electrically coupled to the output of the means for calculating a digest of values, wherein the means for combining uses a pixel by pixel exclusive OR logic operation.

9. The electronic system recited in claim 8 wherein the means for combining is electrically coupled to the means for extracting at least a predetermined bit from the watermarked image block.

10. The electronic system recited in claim 8 further including a decryption means, wherein the decryption means is electrically coupled to the means for extracting at least a predetermined bit from the watermarked image block and the means for combining.

11. An electronic system for extracting a watermark from a digital watermarked image comprising:

means for modifying at least a predetermined bit within an image block of the watermarked image to a predetermined value;

means for extracting at least a predetermined bit from the watermarked image block;

means for calculating a digest of values using a cryptographic hash function, wherein a user key, an image width, an image height and the modified image block are inputs tot he means for calculating a digest of values, wherein the output of the means for calculating a digest of values using a cryptographic hash function is a hashed output, wherein the means for modifying at least a predetermined bit of the watermarked image is electrically coupled to the means for calculating a digest of values wherein the means for modifying at least a predetermined bit to a predetermined value modifies the least significant bit of the selected group of pixels within the image block; and

means for combining, wherein the means for combining is electrically coupled to the means for calculating a digest of values, wherein the means for combining uses a pixel by pixel exclusive OR logic operation.

12. A method for inserting a watermark into a digital image including the steps of:

partitioning an image block X_r into at least one non-overlapping I×

J block;

for each I×

J block, modifying at least a predetermined bit of each I×

J block to a predetermined value, wherein the modified image block is X_r;

calculating a digest of the values using a cryptographic hash function wherein a user key, an image width, an image height and the modified image block are inputs to the means it, for calculating a digest of values;

combining the hashed output calculated in the previous step with a watermark bitmap B_r, using a pixel by pixel exclusive or logic operation, wherein the output of the step of combining the hashed output with a watermark B_r is a combined image block C_r; and

inserting a first image block into the modified image X_r.

13. The method recited in claim 12 wherein the first image block is the combined image block C_r.

14. The method recited in claim 12 wherein the first image block is an encrypted image block W_r.

15. The method recited in claim 12 further including the step of encrypting the combined image block, wherein the result of encrypting the combined image block is the encrypted image block W_r.

16. The method recited in claim 12 wherein the at least one predetermined bit of the image block X_r is modified by discarding the predetermined bit.

17. The method recited in claim 12 wherein for the step of modifying at least one predetermined bit of the image block X_r a plurality of bits are modified by setting the plurality of bits to predetermined values.

18. The method recited in claim 12 wherein the predetermined bit modified is the LSB within image block X_r.

19. A method for extracting a watermark into a digital image including the steps of:

for each partitioned non-overlapping I×

J block of a watermarked image X_r, modifying at least a predetermined bit of each I×

J block to a predetermined value, wherein the modified image block is Z_r;

calculating a digest of the values using a cryptographic hash function, including providing a user key, an image width, an image height and the modified image block input to the means for calculating a digest of values;

for each I×

J block, extracting at least a predetermined bit from the watermarked image X_r;

decrypting the output of the previous step using a public key decryption function,

combining the output of the cryptographic hash function with the decrypted image of the previous step, including using a pixel by pixel exclusive OR logic operation.

20. The method recited in claim 19 wherein the predetermined bit modified is the LSB within image block X_r.

21. An electronic system for inserting a watermark into a digital image, comprising:

a system for modifying at least one predetermined bit within an image block X_r to a predetermined value, wherein the modified image block is X_r;

a system for calculating a digest of values using a cryptographic hash function, wherein a user key, an image width, an image height and the modified image block are inputs to the means for calculating a digest of values, wherein the output of the system for calculating a digest of values is a hashed output, wherein the system for modifying at least one predetermined bit of the image block is electrically coupled to the system for calculating a digest of values;

a system for combining the hashed output with a watermark, wherein the system for combining uses a pixel by pixel exclusive OR logic operation, wherein the system for combining the hashed output with a watermark is electrically coupled to the output of the system for calculating a digest of values, wherein the output of the system for combining is a combined image block C_r; and

a system for inserting a first image block into the modified image block X_r, wherein the system for inserting the first image block into the modified image block X_r, is electrically coupled to the system for modifying at least one predetermined bit of the image block.

22. The electronic system recited in claim 21, wherein the first image block is the combined image block C_r.

23. The electronic system recited in claim 21, wherein the first image block is an encrypted image block W_r.

24. The electronic system recited in claim 21, wherein the system for combining the hashed output with a watermark is electrically coupled to the system for inserting the first image block into the modified image block X_r.

25. An electronic system for inserting a watermark into a digital image, comprising;

a system for modifying at least one predetermined bit within an image block X_r to a predetermined value, wherein the modified image block is X_r;

a system for calculating a digest of values using a cryptographic hash function, wherein a user key, an image width, an image height and the modified image block are inputs to the system for calculating a digest of values, wherein the system for calculating a digest of values is a hashed output, wherein the system for modifying at least one predetermined bit of the image block is electrically coupled to the system for calculating a digest of values wherein the system for modifying at least one predetermined bit modifies the LSB within the image block X_r;

a system for combining the hashed output with a watermark, wherein the system for combining uses a pixel by pixel XOR logic block, wherein the system for combining the hashed output with a watermark is electrically coupled to the system for calculating a digest of values, wherein the output of the system for combining is a combined image block; and

a system for inserting a first image block into the modified image block X_r, wherein the system for inserting the first image block into the modified image block X_r is electrically coupled to the system for modifying at least one predetermined bit of the image block.

26. The electronic system recited in claim 25, wherein the system for modifying at least a predetermined bit to a predetermined value modifies the at least one predetermined bit independently for each color plane of the image block.

27. The electronic system recited in claim 25, further including an encryption system, wherein the encryption system is electrically coupled to both the system for combining the hashed output with a watermark and the system for inserting a first image block into the modified image block X_r.

28. An electronic system for extracting a watermark from a digital watermarked image comprising:

a system for modifying at least a predetermined bit within an image block of the watermarked image to a predetermined value;

a system for extracting at least a predetermined bit from the watermarked image block,

a system for calculating a digest of values using a cryptographic hash function, wherein a user key, an image width, an image height and the modified image block are inputs to the system for calculating a digest of values, wherein the output of the system for calculating a digest of values using a cryptographic hash function is a hashed output, wherein the system for modifying at least a predetermined bit of the watermarked image is electrically coupled to the system for calculating a digest of values; and

a system for combining, wherein the system for combining uses a pixel by pixel exclusive OR logic operation, wherein the system for combining is electrically coupled to the output of the system for calculating a digest of values.

29. The electronic system recited in claim 28, wherein the system for combining is electrically coupled to the system for extracting at least a predetermined bit from the watermarked image block.

30. The electronic system recited in claim 28, further including a decryption system, wherein the decryption system is electrically coupled to the system for extracting at least a predetermined bit from the watermarked image block and the system for combining.

31. An electronic system for extracting a watermark from a digital watermarked image comprising:

a system for modifying at least a predetermined bit within an image block of the watermarked image to a predetermined value;

a system for extracting at least a predetermined bit from the watermarked image block;

a system for calculating a digest of values using a cryptographic hash function, wherein a user key, an image width, an image height and the modified image block are inputs to the system for calculating a digest of values, wherein the output of the system for calculating a digest of values using a cryptographic hash function is a hashed output, wherein the system for modifying at least a predetermined bit of the watermarked image is electrically coupled to the system for calculating a digest of values, wherein the system for modifying at least a predetermined bit to a predetermined value modifies the least significant bit within the image block; and

a system for combining, wherein the system for combining uses a pixel by pixel exclusive OR logic operation, wherein the system for combining is electrically coupled to the system for calculating a digest of values.