1. A method for constructing a template image for recognition, comprising the steps of: obtaining a plurality of digitized images that belong to n categories, each image including location and gray level information of pixels of the image and category information of the image; for all categories, abstracting common features Ai for images belonging to a category Di (0<i≦n); comparing common features Ai of said category Di with common features Aj of a predetermined number m of categories other than category Di (0<j≦m≦n−1), to obtain discriminating features Σ(Aj T Ai) for category Di; and including features Σ(Aj T Ai) into said common features Ai to obtain template image Ai* for category Di.