Local affine transform invariant image watermarking by Krawtchouk moment invariants
Zhang Li, W.W. Xiao, Ji Zhang · IET Information Security · 2007
Image watermarking has become a popular technique for authentication and copyright protection. However, many proposed image watermarking techniques are sensitive to affine transforms, such as rotation, scaling and translation. Here, a local affine transform invariant watermarking is designed and tested against attacks performed by Stirmark using the Krawtchouk moment invariants. Watermark is inserted into the perceptually significant Krawtchouk moment invariants of the original image, and watermarking based on Krawtchouk moment invariants are local, that is, the embedded watermark affects only a selected portion of the original image, the position of which can be decided by the user. This, in effect, permits the watermark to be embedded at the portion of the image which is most significant information-wise. This also means that the watermark is especially robust to cropping. Independent component analysis (ICA) is utilised by detector to extract the perfect watermark blindly. The computational aspects of the proposed watermarking are also discussed in detail. Experimental results have demonstrated that the proposed watermarking technique has a good robustness against other attacks performed by Stirmark including affine transform, cropping, filtering, image compression and random geometric distortions. It is indicated that the proposed watermarking has superior advantages over the existing ones in many aspects.