@orangey03 – Wow, I had never heard that about mailing a work to yourself. I guess that would serve as proof, but I think that visiting the copyright website is still the safest route.
I write novels, but I write under a pen name. If one of my books gets famous one day, I want to be absolutely sure that no one else tries to claim that they are the writer and gets away with it. When I applied for exclusive rights, I supplied both my real name and my pen name.
If some movie producer ever showed interest in my book, I would want to be sure that I had exclusive rights to sell the book as a movie. I wouldn't want to miss out on all that money!