1. A method to identify image differences, the method comprising: electronically determining whether a difference between a first block of pixels of a sample image and a second block of pixels of a reference image is resolvable using a transformation operation; when the difference between the first and second blocks is determined to be unresolvable, but not when the difference between the first and second blocks is determined to be resolvable, including the first block in an unresolved difference region of the sample image; and electronically generating a difference signature representative of the unresolved difference region, the difference signature to identify the unresolved difference region of the sample image.