Robust digital image watermarking based on subsampling

This paper presents a robust digital watermarking scheme for copyright protection of digital images. Four subimages are obtained from the host image by using subsampling. A binary watermark image is permutated using chaotic map and then is embedded into the DCT coefficients of two of the subimages which are selected according to a random coordinates sequence generated by a secret key. Watermark extraction is simply by comparing the DCT coefficients of the watermarked subimages and does not need original image. Experimental results show good robustness and security of the proposed scheme.