Similarly, if you have proof but do not present a legal challenge, then someone else might get away with claiming the copyright. So, copyright is only as good as your proof and your willingness to defend it.

I have a friend who is a songwriter, Every time that he wrote a song that he was happy with, (much less frequently than every time he wrote a song) he used to turn up my house with a small reel-to-reel tape for me to record him singing the song on my tape recorder. He would them put the tape in one of those strong registered mail envelopes that the Post Office used to sell - don't know if they still do - and post it to himself.