An image-quality guaranteed watermarking scheme with spreading spectrum of watermark

This paper proposes a novel watermarking scheme that spreads spectrum of a watermark by selecting a different DCT (discrete cosine transform) coefficient each block in embedding a watermark element. This scheme generates watermarked images with desired objective image-quality in terms of the peak signal-to-noise ratio, and extracts an embedded watermark without any reference images. By randomizing the coefficient selected in each block, the proposed scheme is able to change the subjective image-quality of a watermarked image independently of the objective image-quality as well as malicious detection of the embedding coefficients becomes difficult.