A low cost perceptive digital picture watermarking method

This paper presents an additive watermarking technique for grey scale pictures, which can be extended to video sequences. It consists of embedding secretly a copyright information (a binary code) in the picture without degrading its quality. Those bits are encoded through the phase of Maximal Length Sequences (MLS). MLS are sequences having good correlation properties, which means that the result of the autocorrelation is far greater than crosscorrelations, i.e. correlations made with shifted version of this sequence. This embedding is performed line by line going from the top to the bottom of the picture as the objective was to implement a low cost and real time embedding method able to work for common video equipments. The very embedding process is underlain by a masking criterion that guarantees the invisibility of the watermark. This perceptive criterion, deduced from physiological and psychophysic studies, has already proved its efficiency in a previously presented paper (Conference SPIE '96). It is combined with an edge and texture discrimination to determine the embedding level of the MLS, whose bits are actually spread over 32 by 8 pixel squares. Eventually, some preliminary results are presented, which analyze the efficacy of the decoding as well as the resistance of the watermark towards compression and robustness against malevolent treatments.