Robust dynamic block-based image watermarking in DWT domain

Digital watermarking is a method for protecting copyrighted materials such as digital images. This paper presents a new watermark embedding technique based on Discrete Wavelet Transform (DWT) for hiding little but important information in images. In order to conform to human perception characteristics, this approach uses three sub-bands of DWT. The main goal of the proposed scheme is to apply a dynamic blocking instead of a static one for selecting the positions of the embedding watermark bits. Dynamic blocking is applied to those pixels which are related to strong edges where these pixels are obtained from HL and LH sub-bands of DWT. Because watermark bits are embedding several times and their embedding position depend to the selected cover image, our proposed scheme is naturally secure to block based local attacks, and therefore, it is suitable for maps and natural images. Robustness of this technique is because of the fact that during the extracting phase, one of these two sub-bands, i.e. HL or LH, has a role of backup for the other one. Experimental results show the high validity and good transparency of this new approach.