To surely extract recognition object images by effectively removing the other images from image data.

The following parts are functioned: a contour extraction part which performs contour extraction processing for extracting a contour of a pixel group which has pixel information meeting a prescribed pixel condition and consists of a consecutive pixels, from image data; a contour judgment part which judges whether the trajectory of the contour extracted by the contour extraction part meets a prescribed trajectory condition or not; a pixel information change means which changes pixel information of respective pixels constituting the contour extracted by the contour extraction part, to another pixel information meeting the prescribed pixel condition when the contour judgment part judges that the trajectory of the contour doesn't meet the prescribed trajectory condition; and a recognition object image extraction part which extracts image data corresponding to an inside area of the contour extracted by the contour extraction part, as the recognition object image when the contour judgment part judges that the trajectory of the contour meets the prescribed trajectory condition.