Originally, copyright law in the United States was protected by common law that originated in England. Later the U.S. Congress passed the Copyright Act -- found in Title 17 of the U.S. Code -- and amended it several times. The Copyright Act modified but did not repeal common law. In addition, the U.S. has signed copyright treaties with other nations. This legal background has given rise to several different types of copyright law.
Your work obtains an "automatic copyright" as soon as you reduce it to a tangible medium -- such as recording a song -- as long as it is original. You may then sue an infringing party for any damages his infringement caused you. The main disadvantage of an automatic copyright is that it is often difficult to prove damages. To prove that you were damaged by someone who uploaded your copyrighted song to a popular website, for example, you might have to show that a certain number of people listened to your song on the website instead of purchasing it from you.
Works for Hire
A work for hire copyright is created when one party agrees to create a work in exchange for payment from another party. The moment the work is created, it belongs to the party who paid for the work rather than the party who created it. An example of a work for hire might be a magazine feature article written by a writer who signed a work-for-hire agreement prior to his employment with the magazine.
The U.S. Copyright Office will register the work of copyright holders who apply for registration. Once a work is registered, the copyright holder is automatically entitled to sue an infringing party in federal court. He does not need to prove damages, and he can collect up to $150,000 per work in statutory fines from the infringing party, depending on the discretion of the court. Alternatively, the copyright holder may still sue for damages if he can prove the amount of damages.
International Copyright Treaties
Two major copyright treaties exist: the Berne Convention and the Universal Copyright Convention. Most of the nations of the world have signed at least one of these two treaties -- and the United States has signed both. These treaties allow works created in one nation to be copyrighted in other treaty nations. Protection abroad, however, is subject to the copyright law of the nation that grants copyright protection. For example, a work created in the United States is protected in Canada, but Canadian law rather than U.S. law determines the date the copyright expires.