1. A document processing apparatus comprising: a character segmentation unit that segments a plurality of character images from a document image; a character image classifying unit that classifies the character images to categories corresponding to each of the character images; an average character image obtaining unit that obtains average character images for each of the categories of the character images classified by the character image classifying unit; a character recognizing unit that performs a character recognition to a character contained in each of the average character images; and an output unit that outputs character discriminating information as a character recognition result obtained by the character recognizing unit.