A feature point is a point at which a correlation value is greater than a threshold value, wherein the correlation value is calculated between a template and partial image within an area that is one portion of each genuine tablet image. With regard to a cross-check image, which represents a tablet the authenticity of which is to be verified, a correlation value is calculated between a partial image within an area that is one portion of the cross-check image and the template image, and multiple feature points of the cross-check image at which the calculated correlation value is greater than a predetermined threshold value are extracted. The degree of similarity between the cross-check image and the genuine tablet image is calculated using a geometric characteristic of the extracted multiple feature points and a geometric characteristic of the stored multiple feature points of the genuine tablet image.