An Effective Authenticating Method On The Compressed Image Data

In this paper, we propose an effective watermarking method dedicated to authenticating the compressed image data. By exploiting the characteristics of JPEG compressed data, we compare the quantized with the non-quantized DCT coefficients for finding the embedding positions. A block-classification strategy is used for classifying 8 times 8 DCT blocks into key-blocks and flat-blocks in order to hide different watermarks into the positions mentioned above. Experimental results show that the efficacy of the proposed approach for JPEG images with about 75% to 90% compression ratio and the watermarked image still maintains a PSNR over 37dB, and only a slight overhead in bit-streams is introduced