At this point I have lost track how many times I have been given inaccurate counsel from other well-meaning people, such as, "Make sure you copyright that so nobody can steal it," or "If you put it online then you give up your rights and it becomes public property." Such advice will only ever come from people who don't actually understand copyright laws. When it comes to copyright issues and navigating them, the only advice worth following is advice that can be backed up by law. If you receive advice that can't be backed up by legitimate copyright law then the advice is simply someone's opinion.
In this particular realm, it will likely be in your best interest to simply do your own research and understand, for yourself, what the copyright laws are for where you live. For the purposes of this article we will be looking at, and linking to, the copyright laws specific to the United States of America. For individuals both in the U.S. and outside of it, in order to understand what laws protect your works in other countries you will have to look up the laws for the specific country in which you need copyright protection.
From my experience, there seems to be a misunderstanding as to when the copyright comes into play. In a nutshell, under the Federal Copyright Act of 1976, all photographs are protected by copyright from the very moment of creation. If you would like an in-depth description of your rights as a photographer, you can read through all the government documentation that outlines the specifics of the actual laws concerning subject matter and scope of copyright. There are distinct differences between ownerships that need to be understood. For client work, understanding the intricacies and differences between the possible ownerships of copyrights is something that needs to be clarified up front (this is where your contracts come in handy).
The following is a direct quote from the U.S. Copyright Office outlining the copyright laws for the United States.
Ownership of a ‘copy’ of a photograph — the tangible embodiment of the ‘work’ — is distinct from the ‘work’ itself — the intangible intellectual property. The owner of the ‘work’ is generally the photographer or, in certain situations, the employer of the photographer. Even if a person hires a photographer to take pictures of a wedding, for example, the photographer will own the copyright in the photographs unless the copyright in the photographs is transferred, in writing and signed by the copyright owner, to another person. The subject of the photograph generally has nothing to do with the ownership of the copyright in the photograph.
In general, what that means for you, the photographer, is that your images are copyrighted automatically simply by you clicking the shutter. The only way that changes if you have a specific arrangement with your client, documented and signed by both parties, before creating the photographs. If it isn't documented and signed before the creation of the images, then a legally binding document must be signed that outlines the transfer, either in whole or in part, of the copyright from the photographer to whoever the recipient is.
Going to the extent of legally registering the copyrights for your photographs is not an obligatory step for protecting yourself. Registering your copyrights will make things easier should you enter a litigation situation, or for claiming damages, but you do not relinquish your copyrights to any image simply because it isn't registered.
Below are some of the most helpful sources that can help you gain a more advanced knowledge of copyrights and the laws protecting them: