Comments on "An SVD-based watermarking scheme for protecting rightful ownership"

In a recent paper by Tan and Liu [1], a watermarking algorithm for digital images based on singular value decomposition (SVD) is proposed. This comment demonstrates that this watermarking algorithm is fundamentally flawed in that the extracted watermark is not the embedded watermark but determined by the reference watermark. The reference watermark generates the pair of SVD matrices employed in the watermark detector. In the watermark detection stage, the fact that the employed SVD matrices depend on the reference watermark biases the false positive detection rate such that it has a probability of one. Hence, any reference watermark that is being searched for in an arbitrary image can be found. Both theoretical analysis and experimental results are given to support our conclusion.