Abstract: An image spatial semi-fragile watermarking algorithm was proposed by exploiting the contrast sensitivity of the host image. The watermark bit was embedded into the host image by adaptive least significant bit (LSB) substitulion and the bit plane of each pixel for data embedding was determined by the contrast sensitivity. The algorithm deduced theoretically the adaptive threshold for automatic tampering detection and location, and has good transparency because of the exploiting of the contrast sensitivity. Experimental results show that the proposed scheme has good robustness against admissible incidental attacks, while it is sensitive to malicious attacks, and even can localize the tampered region precisely. In addition, this algorithm can distinguish effectively incidental attacks from malicious ones and outperforms other semi-fragile watermarking algorithms at the classification of attacks.

Key words: Semi fragile watcrmarking,Contrast sensitivity,Image authentication, Tamper detection