In a method for identifying discrepancy of a captured digital image of an object, a standard image of the object is obtained. A first difference value between an IAED value of the digital image and an IAED value of the standard image is calculated. Both the two images are divided into N pixel blocks. A second difference value between an IAED value of each pixel block of the digital image and an IAED value of each pixel block of the standard image is calculated. A coefficient T is generated for comparing the digital image and the standard image, and each block of the digital image is compared with each pixel block of the standard image. The same pixel blocks between the digital image and the standard image are eliminated from the digital image, and a discrepant image is generated according to remaining pixel blocks of the digital image.