1. A digital image comparison method useful in imaging software development, comprising: (a) generating test digital images from print data using imaging software under development; (b) generating reference digital images from the print data using reference software; (c) automatically comparing the test digital images and the reference digital images using an image comparison program executed by a computer; and (d) presenting comparison result to a human operator, wherein the step (c) comprises: (c1) dividing the test digital image and the reference digital image into a plurality of test tiles and reference tiles, each test tile corresponding to a reference tile; (c2) performing a pixel-by-pixel comparison of each test tile and the corresponding reference tile; (c3) generating a difference tile representing differences between each test tile and the corresponding reference tile at least when the test tile and the reference tile are different, wherein the difference tile is an image that consists of pixels each of which represents a difference between a corresponding pixel of the test tile and a corresponding pixel of the reference; and (c4) storing each difference tile with the corresponding test tile and reference tile in an image file, wherein all of the test tile, the reference tile and the difference tile are being presented in a state of individual tiles each divided from an original entire image and laid-out adjacent to each other in a page of the image file.