the i3 3220 has 2 cores with hyper-threading
whereas the i5 has 4 real cores.
logically i5 should give better performance, but if image editing is all you do, and you can't spend a lot, i say go for the i3 (since W7 supports HT) and use the leftover money to get lots of (8 GB at-least) of hi speed RAM. 1866 or even 2k+ MHz.. Most image editing SW's that i know benefit massively from large amounts of RAM.
