A robust watermark authentication technique based on Weber's descriptor

One of the major challenges in the field of digital image watermarking is to authenticate the presence of watermark in the watermarked image even after it has been transformed intentionally or unintentionally. Transformation can be geometric-like rotation, scaling, and translation of image or may be due to any signal processing attack like noise corruption, compression, and cropping of image. There may also be some photometric changes, for example change in the brightness of watermarked image during transmission, due to which it becomes difficult to validate whether received image is watermarked or not. Illumination invariance property of Weber's descriptor has engrossed to use it in the proposed watermark authentication technique. Weber's descriptor is a descriptor based on two parameters of a pixel, differential excitation and orientation. These parameters are computed using the relative intensity value of neighbor pixels and current pixel. This descriptor remains the same even after intensity changes due to the contribution of all neighbor pixel's intensity in its computation. It is also known to be robust to scaling and rotation. Experimental results show that the proposed watermarking technique is able to authenticate the presence of watermark in the watermarked image even when it is distorted due to geometric and photometric attacks. In addition to this, it is found to be robust against noise, cropping, and compression attacks.