Digital watermarking is a process whereby random information is encoded into an image in such a way that the additional payload is indiscernible to the image observer. In this Paper, three typical watermarking techniques are compared and tested extensively, which not only include the private system, the semi-private system but also the public schemes. The comparisons mainly focus on the evaluation of robustness and visual image quality. The results show that the chosen schemes do not have the same behavior and no method has all desirable characteristics. Consequently, we conclude that evaluation of a watermarking algorithm is difficult without first indicating the context in which it is to be applied.
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