copy rights
In Apple vs. Franklin computers, the supreme court upheld that an intellectual property was only 10% original, and therefor you had to change 10% of the original property to not infringe on someone's copyrights. In this case, specifically, Franklin had copied the memory chips of an Apple computer to make an Apple compatable. The courts ruled Franklin could copy the code as long as they changed 10% of it.
As far as I know, no one in the art community has used or challenged this, but I am also certain at least in the music community, that no DJ who has "masked" or manipulated a sample has been sued yet. Only the people who make straight samples that are recognizeable as part of the original song.
There is also a question of whether you are trying to benifit financially by being identified with someone's work. If it is questionable whether a reasonable person could make the connection? Like, if you used likenesses of Andy Warhol's paintings to create the impression that Andy was somehow involved in your film. Then they can rule you are seeking to benifit from it.
I took a class on this 2 years ago and unless something has changed since then, it is still 73 years as a rule of thumb. The laws changed in the 70's but only affects works less than 73 years old, which is why they use this as a rule of thumb. The date is not from the time it was published, but from the time of the last publishing after the author's/artists' death. That depending, there are works less than 73 years that are no longer protected.
So technically, if you can prove there is a 10% difference between the image you used and the image you "sampled" you are technically ok. And if no one except an art expert can recognize it, and you make no effort to associate your film with the artist, they are going to have a hard time going after you. And if you form an LLC or Subchapter S for your film company to protect you, and you don't really make any money as most films don't, they can't really sue you for anything, can they?
Max Krueger
http://freakoutfilms.com