The art that I used came from various artbooks. Darkstalkers Tribute for the front image and Capcom Design Works for the back image.
I've also got a few obscure games that I need to case...games like Future Cop LAPD, Ball Breakers, Robo Pit 2 and a few others that I'm just not going to find art for online. In this case, I have two choices - find unrelated images that look like they could fit, or just edit whatever source images I have to make them usable.