Many digital watermarks now available for images are sensitive to geometric distortions

which particularly prevent blind detection of a public watermark. In this paper

a watermarking algorithm based on singular value decomposition (SVD) is proposed

which is robust to common geometric distortions. The watermark is embedded into image's singular values. By the algebraic properties of SVD

it is proved rigorously that singular values of the watermarked image are invariant when it goes through the geometric distortions of transpose

mirror reflection

rotation

scale

and translation. Experimental results show that the watermarking algorithm performs well in robustness. The embedded watermark can be detected reliably

following these geometric distortions

usual signal processing

or JPEG compression.