Actually, copyrights belong to the photographer - automatically - the second you click the picture. The photographer is not required to do anything to earn that copyright. The copyright IS AUTOMATIC.
If you also filed your photos with the US copyright office BEFORE the infringement, you are allowed to sue for extra damages. I am not an attorney -- I'm only trying to provide a starting point for your own research.
Proving you own the image might be harder - document your work if copyright is important to you.
If you upload your images to a site, pay attention to the legal agreements. What are you giving up? If you use Creating Commons, pay attention to what you are giving up or gaining.
I recommend using a program, such as PaintShop, to add a small invisible logo to pictures. I also take pictures a little larger than needed, and crop the version to be uploaded. The uncropped version helps prove that you own the picture.
My preference:
I'm not concerned about getting credit for an image, and I have posted items without any type of copyright or credit notice. I like sharing information. However, it's also important to prevent (legal) abusers (such as Getty Images) from swiping public domain images and putting them up for sale.