1. An image processing method comprising the steps of: reading an original placed on an original platen; executing a filtering process to extract a contour on the read image; extracting a contour group in broken lines from the image having the filtering process executed; forming one contour from the contour group in broken lines; determining an area of the original from the contours obtained in the filtering execution step and the forming step; and extracting an image of the determined original area from the read image.