All Artists need to know their rights and not let them get eroded or violated by unscrupulous persons.
Copyright begins the moment the work is created in tangible form by the author. This applies to pictorial works, audio works, choreographed works, literary works, motion pictures, dramatic works, sculptural works, performance works and so on.
Owning a piece of artwork is NOT the same as owning the copyright!
There are a few very useful websites out there with loads of info on copyrights:
Here's the official US site: http://www.copyright.gov/
See also:
Volunteer Lawyers for the Arts: http://www.vlany.org/index.php
copyright alliance: http://www.copyrightalliance.org/