There are three compelling reasons to watermark your photos: (1) It is an obvious visual cue to a potential infringer that the photographer wants to protect her rights, (2) It enables those who see your work to find you to license it, and (3) If the watermark is removed, the photographer may receive additional damages in the case of an infringement.
In the U.S. Copyright Law, under section 1202, copyright holders are granted up to $25,000 in damages if an infringement occurs where the wrongful party removed the watermark. This money is in addition to damages for the infringement, and it provides for attorneys fees, and it can be collected even where the photographer did not register her images. More on the legal aspects of watermarking on the FANTASTIC PhotoAttorney Blog.improvephotography.com/6394/ho…
To copyright your photo, you can go about it two ways: the lazy, free way or the legal way. According to the Berne Convention (which I recommend reading so you better understand what it really covers and how it legally protects you), as soon as you press down the shutter on your camera you own the image that creates. The copyright is automatic and instantly yours. You own the copyright of that photograph for a minimum of 25 years (duration of copyright depends on the medium). It does also state that people can use* your work as long as they credit you with it. *Please note that this only extends to situations involving teaching purposes or journalistic reporting of current events in print or broadcast as per the Berne Convention sections 10, 10bis and 11bis(3) of Article 9(2). The Berne Convention does not ensure you will get paid every time someone else uses your photo. It does not clarify how you are to prove that the photo, if it were to come into question, would be proven as yours.
The copyrights as per the Berne Convention are international. "The Berne Convention for the Protection of Literary and Artistic Works, usually known as the Berne Convention, is an international agreement governing copyright, which was first accepted in Berne, Switzerland, in 1886." (Wikipedia)
Well, I've just discovered the Creative Commons Website:
*"Creative Commons helps you share your knowledge and creativity with the world.Creative Commons develops, supports, and stewards legal and technicalinfrastructure that maximizes digital creativity, sharing, andinnovation."
*"There is no registration to use the Creative Commons licenses. Licensing a work is as simple as selecting which of the six licenses best meets your goals, and then marking your work in some way so that others know that you have chosen to release the work under the terms of that license."
*(Both quotes are directly from the website.)
I strongly suggest that you check out these sites.