An information hiding system such as a digital-watermark information system has an embedding side and an extracting side for recognizing an identical character string in which digital-watermark information is embedded, and the extracting side reliably extracts all digital-watermark information from the character string. In order to realize this, an image processing method of the present invention includes a determining step of determining whether a predetermined distance between each target character and an adjoining character can be maintained if any digital-watermark information which may be embedded in the target character is actually embedded; and a setting step of setting an object which is to be embedded with digital-watermark information according to the determination result.