A Robust Digital Blind Image Watermarking Based on Spread Spectrum in DCT Domain

This paper presents a new method in blind digital watermarking based on Discrete Cosine Transform (DCT). The image is quantized in 8×8 blocks, a DCT transform is applied to each block and a collection containing the first two AC coefficients from the DCT transform of the 8×8 image block (coefficient (2,1) and (1,2)) and the bias member, which is zero, is set. The watermark is coded in spread spectrum. In this method for each watermark code the nearest member of the collection (which has not been selected) will be chosen. If the chosen member is not the bias member, the watermark code will replace the AC coefficient in the DCT transform of the image block. While the security of this method is acceptable, the simulation results show a high performance in transparency, resistance and capacity in comparison with similar methods.