Grab a copy of the default Steve skin and just replace all the pixels that you didn't intend to change with that. Basically put it on a layer below your modified one, in the same location, then select every pixel you intentionally changed that you know of, invert the selection, press delete, and merge the two layers. It should be faster than trying to figure out changed pixels.
Alternatively, an easy way to tell what's different is to put the Steve skin in the same spot on a layer above and set the layer's blending method to XOR. That will show all differences in pixels. I also have a plugin somewhere called Image Difference that basically did the same thing.