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; and (c4) storing each difference tile with the corresponding test tile and reference tile in an image file, the tiles being adjacent to each other in the image file.