D.A. posted this. He's not talking specifically about filmmaking, but about fan art. Still, what he does say about copyright, trademark, and fair use etc seems nicely general and clearly explained. He used to be a "hired gun(?)" for Paramount. It's pretty interesting what he has to say about using public domain stuff: in a nut shell, he says that if you want to use something that is supposedly public domain in a serious way, then talk to a lawyer to be sure. 
https://www.youtube.com/watch?v=xKBsTUjd910
https://www.youtube.com/watch?v=xKBsTUjd910
