When editing something like a product photo, where the background is supposed to be all the same color and share, it would be really handy to have the avbility to "compare corners" somehow to ensure that you are even across the image. I'm picturing a square divided into 4, showing as much or as little of each of the corrisponding corner of the image that would allow you to see just how close or off each of the corners of the image is.