Authentication of lossy compressed video data by semifragile watermarking

This paper proposes an effective technique to detect and locate alterations of the tampered frame, whether it is stored again into original bit-streams or not. A block-classification strategy is used to classify DCT-blocks into the flat-block and the normal-block. Simple features of the both blocks are embedded invisibly. The damaging problem of clipping errors caused by normalization in spatial domain can be reduced significantly more than other techniques. Experimental results show that the proposed technique can detect various tampered areas and hence provide an effective image authentication for lossy compressed videos (e.g. H.263), especially for DVR (digital video recorder) security systems.