As long as you're Not making any money off the liscense, you can claim public domain and get away with it. but if you start making money off it, they can sue the crap out of you.
so rule of thumb is : if you're gonna give it away for free, you can use whatever likeness you like.
if you're gonna charge money for it, got to be completely original, or you got to get permission.
Actually, they can still sue you for using copyrighted material. The only way you can use stuff legally (without paying for the rights) is in parody or documentary.
Most places don't care as long as you don't make money, but they could sue you if they wanted to. For instance, Lucasfilm doesn't care about people making Star Wars fanfilms, but they can't make money off it.