Public domain is free as long as the Creative Commons license makes it so. The fair use doctrine for images gets pretty dicey especially when you're earning income on the work. Even giving credit doesn't necessarily cover you.
Fair use for written word is pretty firmly established, for images not so much and for music it's even worse.
When I was researching the use of lyrics for a Christmas Colouring book I was creating about the best advice that could be found short of talking to an IP lawyer was unless a song was in the public domain, don't use anything more than the title on a commercial use.