Digital Watermarking Based on a Gradient Orientation Code

This paper proposes a novel digital watermark based on the gradient orientations of a digital image. The specific features of a digital image can be expressed pixelwise using a 3-bit gradient orientation code (GO code). As the first watermark, the 3-bit GO code, covering 8 gradient directions, are spread and embedded in the three least significant bit (LSB) planes of its RGB color channels. The GO code is used for detecting the tampered region in an image. As a second watermark, we also embed a down-sampled self-image into the three second least significant bit (LSB2) planes of the image. The second watermark, excluding the tampered region, is utilized for recovering the original image. Experimental results show that the proposed method can detect and recover image tamper that occupies slightly more than 50% of an image. The quality of reconstructed images is maintained over PSNR 40dB.