If I write a composition and want to share it with the world, what's the best way to establish that I am its creator? I remember reading a book where you could do something like write it down and mail it to yourself to do this, but I wonder if that's legit and/or how this should be handled in this electronic age?
closed as off topic by Matthew Read♦ Jul 20 '12 at 15:43
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In the USA and most of Europe, you own the copyright on any work you create automatically.
Things get a little bit more complicated when you create things as part of your job while working for an employer, but I assume that's not what you're asking about.
So the formal answer is, you don't have to do anything.
However, the question arises -- what if someone copies your work, and when challenged, they flat-out lie and claim they wrote it before you? It's your word against theirs. If that happens to you, you might wish you'd got some proof of having written it.
Sending yourself a copy in the mail is one old favourite. The idea is that you do not open the envelope until needed; the postmark is a proof of the date.
There are agencies that keep copies of your work and will give evidence to a court of the date when you lodged it. They charge money, of course.
possibly register it with the US copy right office: http://www.copyright.gov/help/faq/faq-register.html
Initially, join your local equivalent of the Performing Rights Society - and register all your songs with them.
Also, publishing to YouTube, Soundcloud, iTunes or other online distribution media will give you a date stamp.
Posting a CD to yourself (or even better, to a certified notary or lawyer) via recorded delivery can also be used as a good piece of evidence if necessary, but in the technological age we live in, it is less useful than it used to be. The world can always google for the first appearance of a work.