A fragile watermarking scheme for image authentication with localization and recovery

A fragile, block-wise, and content-based watermarking for image authentication and recovery is presented. In this scheme, the watermark of each block is an encrypted form of its signature, which includes the block location, a content-feature of another block, and a CRC checksum. While the CRC checksum is to authenticating the signature, the mixture of the location indices of one block with the feature of a randomly selected block complicates the VQ attack. The encryption further strengthens the security. That all security parameters are user dependent and can be computed at both ends individually based on Diffie-Hellman key exchange method makes the scheme not only robust against collage attack but also truly oblivious. The experiments demonstrate that our scheme can detect and localize any tampering of size 8×8 pixels and above and can recover a 40% damaged image to an intelligible one with 24 dB. As for incidentally manipulated images, our scheme can invalidate all the blocks but does not further degrade the images. Comparing with the scheme of Celik et al. (2002), ours has better tamper localization accuracy while trading off 2-3 dB of the PSNR of watermarked images for recovery.