Don't create new image if nothing has changed

[garygreen]

If you did ->guess(100); and didn't apply any operations I would expect it to just copy the image unchanged. Instead it creates a new image (100% of quality of original) -- this doesn't make much sense. Basically I would like to use the cache system to move the image into a 3/4/5/a/3/5/f type location without changing it at all.