Holographic semi-fragile watermarking combined with asymmetric crytography

A semi-fragile watermarking technique, with a Computer Generated Hologram (CGH) coding system of the mark, is introduced and tested. The CGH watermarking is used for image authentication. The hologram of the mark is embedded in the spatial domain by a blind additive embedding technique. The use of holography, to authenticate even small pieces of the original image, is the major novelty ot this paper. In fact, holography allows the hidden data to be resistant to cropping attacks. The proposed methodology is characterized as a blind semifragile authentication technique, since it does not rely on the original image to decide whether the Watermarked Image has been altered or not and at the same time it is able to detect and localize any possible malicious change. Asymmetric cryptography is used to hide the hash information in an unambiguous way (non-repudiation property).