Copyright is a legal right, grounded in the United States Constitution, that gives the owner of copyrighted work the exclusive right to:
Copyright applies for a limited term. The length of that term depends on when the work was first created, whether or not it has been published, and whether the work was first published in the US or abroad.
When the copyright term in a work expires, the work loses copyright protection and enters the public domain.
To determine the copyright term for all other works, consult the Cornell University chart Copyright Term and the Public Domain in the United States.
These works are in the public domain and can be used by anyone for any legal purpose without permission:
Unless you are sure a work falls into one of these categories, you must assume the work is protected by copyright.