Getting pixel value from Picture object is incredibly slow

Something else you could do is just do a quick binary file comparison.... if the files match, then you don't need to do any more processing.

Then, perhaps, take them in 100 x 100 chunks. If a chunk shows a mismatch, then report the problem... perhaps then do the pixel by pixel compare but really, that seems to be on the lines of building a nuclear powered can opener when a simple hand crank one will do