efficient way to compare 2 images?

[madscijr]

squish the two images down to a really small image. If they don't match when they are 2 by 2 pixels they sure aren't going to match when they are say 200 by 200 pixels. 
if it matches keep comparing pixels by pixel in slightly larger scaled image until back up to original size.

This is a creative approach - it's kind of like that collision detection method where you progressively test smaller areas. 

I'll give that code a look when I am back in the IDE. Thanks!