The United States Copyright Office has put together a very clear and easy-to-understand overview of copyrights. Rather than try to improve on a very solid effort, we have excerpted the most relevant sections below.
If you have created an original work and have published it online, you are automatically granted a copyright to that work. Others may not use your work except under very clear guidelines, established in law, even if you did not file for a copyright at the US Copyright Office. If your work has been copied and published online by a copyright infringer, there are remedies available. They are inexpensive and easy to use. If you want to recover damages against someone who has violated your copyright, you must register your work with the US Copyright Office.If someone has copied and republished your content, and you want to stop their web page from appearing on Yahoo, Google, MSN, and the other major search engines, or you want to have their site taken down from the Internet (good enough in most cases), read What can I do about Internet copyright infringement or trademark infringement by another Webmaster? Can plagiarism by another website hurt my rankings? in our Search Engine Marketing FAQ section.
From Copyright Office Basics, United States Copyright Office:
The use of a copyright notice is no longer required under U.S. law, although it is often beneficial. Because prior law did contain such a requirement, however, the use of notice is still relevant to the copyright status of older works.
Notice was required under the 1976 Copyright Act. This requirement was eliminated when the United States adhered to the Berne Convention, effective March 1, 1989. Although works published without notice before that date could have entered the public domain in the United States, the Uruguay Round Agreements Act (URAA) restores copyright in certain foreign works originally published without notice. For further information about copyright amendments in the URAA, request Circular 38b.
The Copyright Office does not take a position on whether copies of works first published with notice before March 1, 1989, which are distributed on or after March 1, 1989, must bear the copyright notice.
Use of the notice may be important because it informs the public that the work is protected by copyright, identifies the copyright owner, and shows the year of first publication. Furthermore, in the event that a work is infringed, if a proper notice of copyright appears on the published copy or copies to which a defendant in a copyright infringement suit had access, then no weight shall be given to such a defendant's interposition of a defense based on innocent infringement in mitigation of actual or statutory damages, except as provided in section 504(c)(2) of the copyright law. Innocent infringement occurs when the infringer did not realize that the work was protected.
The use of the copyright notice is the responsibility of the copyright owner and does not require advance permission from, or registration with, the Copyright Office.
