Copyright rules and laws.
Copyright holders are allowed to copy, display, perform, distribute and sell their own work for public consumption. They are also allowed to create derivative works based on their original work.
The author that creates a work receives exclusive claim to the copyright. If there's multiple authors then they all take the copyright.
Copyrights may be transferred, but the transfer must involve the author or owner, and a written contract. The Copyright Office does not record transfers, so new owners are wise to register the copyright, as that will offer better legal protection.