METHOD AND APPARATUS FOR DIGITAL WATERMARKING OF IMAGES

• US 20010046307A1
• Filed: 04/30/1998
• Published: 11/29/2001
• Est. Priority Date: 04/30/1998
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: WONG, PING WAH
• Granted Patent: US 6,504,941 B2
• Time in Patent Office: Days
• 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:

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

a means for calculating a digest of values using a cryptographic hash function, wherein the means for calculating a digest of value outputs 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;

a means for combining the hashed output with a watermark, 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 a means for inserting the combined image block (C_r) into the modified image block X_r, wherein the means for inserting the combined image block (C_r) into the modified image block X_r is electrically coupled to the means for modifying at least one predetermined bit of the image block.

2. The electronic system recited in

claim 1

wherein the means for combining the hashed output with a watermark is electrically coupled to the means for inserting the combined image block (C_r) into the modified image block X_r.

3. The electronic system recited in

claim 1

further including a public key encryption means, wherein the public key encryption means is electrically coupled to both the means for inserting the combined image block (C_r) into the modified image block X_r and the means for combining the hashed output with a watermark.

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

partitioning the image block X_r into at least one I×

J block;

for each I×

J block, modifying at least a predetermined bit of the block to a predetermined value, wherein the modified image block is X_r;

calculating a digest of the values using a cryptographic hash function;

combining the hashed output calculated in the previous step with a watermark bitmap B_r, wherein the output of the step of combining the hashed output with a watermark B_r is an combined image block C_r;

and inserting the value C_r into the modified image X_r.

5. A method of extracting a watermark from a digital image Y_r, including the steps of:

for each I×

J block, modifying at least a predetermined bit of the watermarked image Y_r to a predetermined value, wherein the modified watermarked image Y_r is Y_r;

extracting at least a predetermined bit from the watermarked image;

calculating a digest of the values using a cryptographic hash function; and

combining the hashed output with the image block E_r.