Multibit data hiding based on CDMA

Most of the existing spread spectrum based watermarking algorithms deal with the embedding and detection of zero bit watermarks. In this paper, we investigate the spread spectrum watermarks with multiple bits of information. For a multibit message to be embedded robustly and securely, a code division multiple access (CDMA) technique is employed. M-ary modulation is adopted to form each multiplexing component. A certain number of wavelet coefficients with large magnitudes are selected and modified by the watermark, which makes the watermark adaptive to the contents of images. The watermark is detected and decoded in an optimum manner based on a generalized Gaussian model. Simulation shows such watermarks can carry a good payload amount and survive a variety of attacks.