Would this question be on-topic here?
http://yro.slashdot.org/story/15/08/16/191215/ask-slashdot-how-to-prove-a-work-is-public-domain
The asker uploaded a very old video to YouTube claiming it is public domain, and YouTube asks him for a "proof" that it is public domain, refusing a simple explanation.
While it is about law, the question is also borderline technical (although it would probably not be on-topic on any other Stackexchange site).