Research in digital watermarking has progressed along two paths. While new watermarking technologies are being developed, some researchers are also investigating di erent ways of attacking digital watermarks. Common attacks to watermarks usually aim to destroy theembedded watermark or to impair its detection. In this paper we propose a conceptually new attack for digitally watermarked images. The proposed attack doesnot destroy anembedded watermark, but copies it from one image to a di erent image. Although this new attack does not destroy awatermark or impair its detection, it creates new challenges, especially when watermarks are used for copyright protection and identi cation. The process of copying the watermark requires neither algorithmic knowledge of the watermarking technology nor the watermarking key. The attack is based on an estimation of the embedded watermark in the spatial domain through a ltering process. The estimate of the watermark is then adapted and inserted into the target image. To illustrate the performance of the proposed attack we applied it to commercial and non-commercial watermarking schemes. The experiments showed that the attack is very e ective in copying a watermark from one image to a di erent image. In addition, we have a closer look at application dependent implications of this new attack
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