The cheapest way, that is legal and will work in a lawsuit if need be. Place all of your images, text, website, etc on a CD. Place your CD in a padded envelope and send it to yourself through USPS, and USPS only via certified mail. When you recieve your certified envelope back, DO NOT open it. Leave it sealed and place it somewhere safe. If the time arises, and you need proof it is your copyrighted material, the court will honor your sealed certified envelope because it has passed through the federal government postal service. The only issue is, as more images are taken and you need to add to your "bank" of materials, you will need to send a new certified letter to yourself with the new material...
Paul