1. An image processing apparatus that performs image processing on image data, comprising: a control unit controlling the image processing apparatus, wherein the control unit executes: an edit-region identifying section identifying a user-specified region in the image data as an edit region; a character-position identifying section recognizing positions of individual characters in the image data; a character-region generating section generating a character area for each of the characters whose positions have been identified by the character-position identifying section; an edit-character-string identifying section identifying an edit character string based on candidate characters that are identified by determining the degree of overlay between the edit region and character region; and a processing unit performing image processing on the edit character string identified by the edit-character-string identifying section; and the edit-character-string identifying section calculates an occupancy ratio, representing how much of the candidate characters occupy a word, for every word overlaid on the edit region, and identifies a word occupied with the candidate characters at an occupancy ratio equal to or greater than a predetermined occupancy threshold as the edit character string.