1. A method of detecting an electronic watermark in a distorted image that constitutes a distortion of an original image in which the electronic watermark is embedded, the method comprising: inputting the distorted image and comparison information, the comparison information including at least one of the original image or information used for embedding the electronic watermark; dividing a domain of the original image into a plurality of patches, based on the comparison information; inputting affine parameters of a predetermined patch from among the patches in the original image; on the basis of the affine parameters, extracting a patch candidate from the distorted image; using a predetermined electronic watermark detection method, judging whether the patch candidate in the distorted image adequately correlates with a neighboring patch in the original image that neighbors the predetermined patch; and when the judging indicates an adequate correlation, outputting a part of the electronic watermark obtained by the predetermined electronic watermark detection method.