Abstract: A technique which can generate stable virtual page marks even in a non-OCR form to stably identify the form. Key segments which can be stably detected within a form are predefined for the detection of virtual page marks, and the virtual page marks (circumscribed rectangle) are generated on the basis of the key segments. Redundancy is bestowed on the detection of the key segments, and substitute segments are defined so as to generate the virtual page marks on the basis of them even in a case where the key segment has failed to be detected due to a stain, a partial lack or the like.