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Basically, if you're not going to be making money off it, don't worry about it, it's no big deal. You'll obviously want to give the artists credit, though.
If it is a big deal, for whatever reason, my only suggestion would be to find some sort of contact information, contact them, and basically spell out your situation. Depending on how "big" the artist is, you may go through a publicist, but either way the most important thing is that you're not making money from it. If you tell them that they'll be like "Okay whatever."