Geometric distortion is known as one of the most difficult attacks to resist. Geometric distortion desynchronizes the location of the watermark and hence causes incorrect watermark detection. In this paper,we propose a geometrically invariant digital watermarking method for color images. In order to synchronize the location for watermark insertion and detection,we use a multi-scale Harris-Laplace detector,by which feature points of a color image can be extracted that are invariant to geometric distortions. Then,the self-adaptive local image region(LIR) detection based on the feature scale theory was considered for watermarking. At each local image region,the watermark is embedded after image normalization. By binding digital watermark with invariant image regions,resilience against geometric distortion can be readily obtained. Our method belongs to the category of blind watermarking techniques,because we do not need the original image during detection. Experimental results show that the proposed color image watermarking is not only invisible and robust against common signal processing such as sharpening,noise adding,and JPEG compression,but also robust against the geometric distortions such as rotation,translation,scaling,row or column removal,shearing,and local random bend.
