1. A method for estimating a number of objects, the method to be implemented by a processing module, and being utilized to estimate a number of a plurality of objects having elongated shapes based on an image of the objects that contains substantially-circular end faces of the objects, the method comprising the steps of: generating a characteristic image based on the image of the objects, the characteristic image containing a plurality of characteristic patterns which are associated with the end faces of the objects; calculating a number of the characteristic patterns based on the characteristic image; and obtaining an estimated number of the objects based on at least the number of the characteristic patterns thus calculated.