ABSTRACT This paper presents an efficient scheme for blind watermark attacking using the concept of matching of the long‐range data. The main idea of the proposed attack is to add plenty of noise to the watermarked image and then try to restore an unwatermarked copy of the noisy image. The aim is to destroy the watermark information without accessing the parameters used during the watermark embedding process. So, it allows our approach to be completely free from any pre‐assumption on the watermarking algorithm or any other parameters that is used during the watermark embedding procedure. Experimental results show the proposed algorithm's superiority over several other traditional watermarking benchmarks such as Stirmark and Optimark. Peak signal‐to‐noise ratio of the watermarked image after applying the proposed attack is more than 45 dB, and the normalized cross‐correlation for the extracted watermark is lower than 0·4, so the watermark is not detectable after our attack. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, we propose a new method for damaging and destroying robust invisible watermarks using an image restoration technique which is called long-range correlation. The restoration technique is based on the concept of the general long-range correlation within natural images. First we add some random noise to the watermarked image, and then by using the restoration technique we restore the destroyed pixels. Restored image has high correlation with the watermarked image but due to some modifications that the restoration process made in the watermarked image, the hidden watermark is destroyed. We have tested the proposed method to attack two recent and robust watermarking methods and the results sound impressive. PSNR of the watermarked image after applying the proposed attack is more than 45 dB and the NC for the extracted watermark is lower than 0.4, so it is not detectable. Moreover, the proposed method does not consider any knowledge about the underlying watermarking algorithm.

In this paper we present a blind low frequency watermarking scheme on gray level images, which is based on DCT transform and spread spectrum communications technique. We compute the DCT of non overlapping 8times8 blocks of the hostimage, then using the DC coefficients of each block we construct a low-resolution approximation image. We apply block based DCT on this approximation image, then a pseudo random noise sequence is added into its high frequencies. For detection, we extract the approximation image from the watermarked image, then the same pseudo random noise sequence is generated, and its correlation is computed with high frequencies of the watermarked approximation image. In our method, higher robustness is obtained because of embedding the watermark in low frequency. In addition, higher imperceptibility is gained by scattering the watermark's bit in different blocks. We evaluated the robustness of the proposed technique against many common attacks such as JPEG compression, additive Gaussian noise and median filter. Compared with related works, our method proved to be highly resistant in cases of compression and additive noise, while preserving high PSNR for the watermarked images.