PURPOSE: To prevent the copying of a confidential document by simple software by extracting a character string from a read original image, and at the time of detecting the overlap of the character part, judging that the original image is a confidential document.

CONSTITUTION: When a picture reader binarizes the image of an original by a prescribed threshold, rectangles which has black dots continue for a certain length are continuously included, these rectangles are recognized as a character. When another area disconnecting a regulated rectangular string appears, whether character strings exist before and after a non-character string or not is used as a decision reference for the existence of a confidential mark. An area of a symbol A is judged as the overlap of a confidential mark expressing a confidential original to a character string and an area of a symbol B is judged as a graphic or a photograph. When a rectangle area larger than each of continued rectangles exists inn a character string, the existence of overlap to the character part is judged and copying is inhibited.