1. An image processing system comprising: an image input section that inputs images which are linked to each other in time series manner; a first character-extracting section that extracts a first character from a first image input by the image input section; a second character-extracting section that extracts a second character from a second image input by the image input section; a difference detecting section that detects a difference between the first character extracted by the first character-extracting section and the second character extracted by the second character-extracting section; a dividing section that divides the difference detected by the difference detecting section in accordance with number of images between the first image and the second image; and a synthesizing section that generates a character string in accordance with the first character extracted by the first character-extracting section and the second character extracted by the second character-extracting section.