1. Watermarking For Image Authentication Presented by San-Hao Wang

2. Outline Introduction Proposed scheme

3. Introduction Properties of an effective authentication  Can determine whether an image has been altered or not  Can locate any alteration made on the image  Can integrate authentication data with host image rather than as a separate data file  The embedded authentication data be invisible  To allow the watermarked image be stored in lossy compression format

4. Proposed Scheme Block diagram of embedding process

5. Proposed Scheme (cont.) Generate a look-up table (LUT)  The table maps every possible value of JPEG coefficient randomly to “1” and “0”  Notation vi : The original coefficient v’i : The marked coefficient bi : The bit to be embed

6. Proposed Scheme (cont.) Embed rules Example

7. Proposed Scheme (cont.)

8. Extract rules  The extraction of the signature is simply by looking up the table

9. Proposed Scheme (cont.) Considerations for minimizing distortion  The run of “1” and “0” entries in the LUT is constrained to avoid excessive modification.  DC coefficient in each block is not changed.  Small valued coefficients are not modified to avoid high frequency distortion.

10. Proposed Scheme (cont.) The above constraints make the number of bits varies from block to block.  We choose to embed one bit per 8*8 by embedding the same bit to all embeddable coefficients in the block.  And extract the bit by majority voting.