1. A method of processing a color image having a plurality of color image data representing a respective pixel, the method comprising the steps of: (a) calculating a first difference between image data D(x) and image data D(x-1) constituting the color image wherein one of the second adjacent two pixels is one of the first adjacent pixels; and the other of the second adjacent two pixels is not the other of the first adjacent two pixels. (b) comparing the difference derived in step (a) with a predetermined value m and detecting a border of the color image when the difference is more than the predetermined value m; (c) when the difference calculated in step (a) is equal to or less than m, checking whether image data D(x) and image data D(x-2) are identical for all of the color components constituting the color image; (d) identifying the color image as a computer-created image or a natural image based on a conclusion of steps (b) and (c); and (e) processing the color image in a different manner depending upon the border detected in the step (b), and the computer-created or natural image identified in the step (d).