It is required to protect the copyrights and the like of partial images which form respective parts of an image obtained by reading an image, exchanged using a print as a medium, by an image scanner or the like. Input image data is divided into a plurality of image regions having different features, digital watermarks, which are embedded in the detected image regions by embedding methods corresponding to the features of the image regions, are extracted, and the availability of the input image is checked on the basis of the extracted digital watermarks.