Low Luminance Smooth Blocks Based Watermarking Scheme in DCT Domain

In this paper, we present a new watermarking algorithm based on low luminance smooth blocks in compressed DCT domain. The blocks are selected by sorting the 8times8 DCT blocks according to the value of DC coefficients and the variance of AC coefficients respectively. The watermark is embedded in these blocks, in which the value of DC and variance of the AC are both small. This scheme depends on shifting the sign of a subset of low-frequency coefficients according to the corresponding watermark information. The watermark extraction can be performed without resorting to original image. Experimental results show that the watermarked images look visually identical to the original, and the watermarks also successfully survive after image processing operations such as image cropping, scaling, filtering and JPEG compression