Adaptive digital image watermarking using variable size of blocks in frequency domain

An adaptive digital image watermarking system considering of the human visual system (HVS) is presented in the frequency domain. The digital watermarks are embedded in selected discrete cosine transform (DCT) coefficients of variable size of blocks. To accommodate the HVS characteristics, the image is divided into variable size of blocks, where each block contains only homogeneous regions. The watermark is inserted by significantly changing the selected DCT coefficients of the block that has great variance or by slightly changing for the stationary block. It is shown that the proposed method has good robustness against several image processing operations without significant degradation of image quality by simulation using various test images.