When I mentioned shorter, I meant shorter than "life of the author plus [bignum] years". My main concern is to figure out how to track down the original author

When I mentioned shorter, I meant shorter than "life of the author plus [bignum] years". My main concern is to figure out how to track down the original author, and also for preservation efforts (esp old films that are rotting away, and no one can archive copies of them legally if the "copyright holder" can't be tracked down, or is unknown). An alternative could be compulsory licensing of unregistered works that are beyond a given age. So that if someone uses it, and no one comes by to claim it is theirs, then all is good. But if a copyright holder shows up (and can prove ownership), then appropriate fees can be transferred at a standard rate.