Robust and geometric invariant watermarking scheme using block and gray-level histograms

As one of the crucial problems in watermarking, robustness against geometric distortion and JPEG compression becomes more than challenging and problematic. In this paper, a robust and geometric invariant watermarking scheme using block histogram and intensity-level histograms is proposed. During watermark embedding procedure, we first compute the number of valid intensity-levels of the given image, and group the pixels into blocks of variable size such that each of which has the same number of intensity-levels. Thus the block histogram is generated for the given image. Then the intensity-level histogram of each block is modified according to the embedding bits of the watermark. During the extraction procedure, the block histogram and intensity-level histogram of each block in the watermarked image are generated in a similar manner and the watermark is decoded according to the distribution of the intensity-level histogram in each block. Experimental results show that the proposed scheme is highly robust against not only JPEG compression, but also geometric attacks and common signal processing such as median filtering. The comparison results also show that the proposed scheme outperforms the existing methods in terms of robustness.