Mail copies or originals of your stuff to yourself and DO NOT OPEN IT. Mark what it is on the outside of the envelope and file it. Then if you have to prove first use, take it to court and DO NOT OPEN IT. When the judge opens it, the postmark proves it was yours before anyone else used it. Cheapest way to prove first use.Oooh! I can't wait to see them all finished! Smart to have watermarks. I hate it when others post my stuff and I am the one that ends up with a copyright claim.
That's one reason I prefer instagram over youtube. Instagram has such a great setup and an amazing algorithm.