@innuendo, good question. I don't imagine any artists would be willing to give permission without getting a cut. Sadly it's being done all the time. Best bet is stock image sites - even those aren't free. If you are making money off of an image (directly or indirectly) that you have not paid for in some form - like a licensing agreement of sorts, you are risking a lawsuit. And you will 99.99999% lose.