a method of recognizing an object based on pattern matching using a gray - scale normalized correlation method includes storing a reference image including a foreground and a background each having a predetermined value of density distribution ; inputting an image of the object which includes a foreground and a background each having a predetermined average value of density distribution ; storing a function for giving the predetermined values of density distribution of the reference image equal to the predetermined average values of density distribution of the input image , respectively ; and obtaining a maximum normalized correlation coefficient between the reference image and the input image using the function .