A storage process section stores, into an exceptional reference image list, discrimination information for discriminating a reference image which permits image processing and a reference image which forbids or restricts image processing. In case where a maximum value of a similarity calculated by a voting process section is not less than a threshold value, a control section determines whether a reference image having a maximum similarity is the reference image which permits image processing or a reference image which forbids or restricts image processing and determines whether or not it is necessary to forbid or restrict image processing with respect to input image data in accordance with a result of the determination. This makes it possible to prevent erroneous determination from forbidding execution of image processing based on input image data or to prevent erroneous determination from allowing execution of image processing based on input image data.