A new semi-fragile watermarking algorithm for image authentication

Semi-fragile watermarking is robust with routine image operation but show high sensitivity with local modification. We take a Scheme based on the sensitivity with initial value of chaotic map and characteristic of DCT. The original image is divided into 8 times 8 blocks firstly, and takes the mean of middle frequency coefficient as initial value of chaotic mapping. The watermark, which generated by several times of the chaotic mapping iteratively, is embedded into the DCT middle frequency coefficient according to coefficient relationship in DCT domain. The proposed scheme can distinguish intentional content modification from incidental tampering. In image authenticating process, there is no need of any information about the original image and watermark, so it will increase the security of watermark and prevent watermark from forging.