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Content Based Image Public Watermarking

In this paper, a content based image public watermarking technique which operates in DCT domain is proposed. First, the 8×8 DCT sub-blocks of the host image are rearranged into a Hilbert sequence in Hilbert scanning order, then two neighboring sub-blocks in the Hilbert sequence is pseudo-randomly selected by using chaotic sequences. Then a watermark with visually recognizable pattern is embedded into the original image by changing the polarity of the corresponding middle-frequency coefficients in the two chosen neighboring sub-blocks, and the watermark is adapted to the image by exploiting the masking characteristics of the human visual system (HVS), thus ensuring the watermark invisibility, and the watermark don’t need the original image. The experimental results show that the proposed algorithm in this paper is robust to common signal processing techniques and some geometric distortions, such as cropping, scaling and rotation. Especially, it achieves high robustness under signal enhancement operations, such as sharpening, contrast enhancement, edge enhancement and h istogram equalization.