Patent ID: 7826637

Claim:
A watermark embedding apparatus, comprising: a processor comprising: a homotopy class calculating unit configured to calculate a homotopy class of an input image to be watermarked; a watermark information class transforming unit configured to calculate a homotopy class of watermark information; and a homotopy class changing unit configured to change at least a portion of the input image based on a topological invariant, wherein the topological invariant is maintained when a local distortion which is a homeomorphism is applied to a topological space formed of a set of points of the input image, the local distortion including a Stirmark attack, the topological invariant corresponding to watermark information to be embedded into the input image, and the local distortion being expressed by functions, each of the functions depending on a position of the points; wherein the homotopy class changing unit is further configured to change said at least said portion of the input image so that the homotopy class of the input image corresponds to the homotopy class of the watermark information.