It is very important that you register copyright for your images. It provides strong legal leverage once you need to make a claim for copyright infringement with a third party.
Step by step tutorial how to register copyright for images at NatureScapes.Net by Carolyn E. Wright, Esq.:
http://www.naturescapes.net/docs/index.php/articles/341
Use this link to get more information about copyright:
http://www.copyright.gov/
Use this link to register an account and start uploading your work:
http://www.copyright.gov/eco/
Information about how to register your images can be found on the Picture Archive Council of America (PACA) web site at:
http://www.pacaoffice.org/registerImage.shtml
More definitions of categories of registrations:
http://www.peterkrogh.com/copyright/main.html
