Über Pixel Comp
With Pixel Comp, You can easily compare the pixels of two images by RGB values and can recognize any differences visually. Also you can alpha-blend the two images to detect any differences. And more, you can compose these images into one and can draw freehand notes on it.
Finally, you can export the composed image to photo album, application document, Dropbox, clipboard, and e-mail attachment (* Full version only).
Sometimes, an unexpected interesting result can be seen by composing images, that is not a primary purpose of this app though. I hope please try various things and enjoy it.