A public-key based watermarking for color image authentication

We present a watermarking scheme for color image authentication based on cryptography. The scheme shows that if even a single bit has been changed, the watermarked image is regarded as unauthentic. Moreover, the scheme indicates the specific locations where changes have been made. To increase the security, the scheme uses two keys for the permutation of the input of the hash function and for the encryption (decryption) of watermark bits during the watermark insertion and extraction procedures, respectively. Results show that our watermark is correctly extracted if there is no change of watermarked image. However, any change of a watermarked image results in no watermark. The pixel changes of the watermarked image are reflected in the extracted watermark, which indicates the attacked area.