A semi-fragile watermarking distinguishing JPEG compression and gray-scale-transformation from malicious manipulation

Semi-fragile watermarking which is robust to given operations and fragile to conscious operations, is a useful authentication technique for digital media. In this paper, a novel semi-fragile image watermarking algorithm that accepts JPEG compression and gray-scale-transformation is proposed. In the proposed algorithm, the properties of JPEG compression, DCT coefficients and gray-scale-transformation are analyzed and used to optimize the embedding parameters especially the quantization step, which can make sure of the robustness and frangibility of the algorithm to given processes and attacks. The robustness and frangibility of the proposed algorithm to given image processes are analyzed, and the results show that the proposed algorithm is very robust to JPEG compression, gray-scale-transformation, and the combination of JPEG compression and gray-scale-transformation, while it is very fragile to malicious attacks, such as cropping, adding signature and median filtering. Namely, the proposed algorithm can distinguish JPEG compression and grayscale-transformation from other attacks accurately.