Semi-fragile watermarking resisting differentiation-based image sharpening

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 differentiation-based image sharpening is proposed. In the proposed algorithm, based on the theory of image sharpening, the pixel value and its rate of change are expressed in exponential form with a base of 2, and the watermark is embedded by modifying the parity of the exponent. 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 different differentiation-based image sharpening, such as horizontal and vertical difference, Robert gradient and Sobel operator, while it is very fragile to other attacks, such as Gauss noise, cropping and neighborhood averaging. Namely, the proposed algorithm can distinguish differentiation-based sharpening from other attacks accurately.