Using Objective-C, is there any way to compare two images and get a % difference value returned?

Question

Using Objective-C, is there any way to compare two images and get a % difference value returned?

For example, one image will have and X in it. Another image will ha

Answer 1

Pixel by pixel comparison wouldn't help if source image size and destination image size is different. In this case the scaling ration should be correct. any other solutions for this?