Log onto any photography forum, and you'll regularly see people complaining about their images being stolen and asking what they can do about it. Hardly any of them have registered their work with the U.S. Copyright Office. This means that the best they can do is to try to recover actual damages, which in most cases, is a negligible amount. Once your image is registered, however, you can sue for up to $150,000 per infraction, plus attorney's fees. In addition, if you've attached a watermark or copyright notice to your image, and the violator has intentionally removed it, you can sue for up to $25,000, plus attorney's fees, for each infraction.
So ask yourself, is it worth spending only $55 to protect all the images you've published within a given year?
A couple of years ago, I published a step by step guide to this process on Medium. Since then, the US Copyright Office, or ECO for short, has modified some of its procedures, so I thought it would be useful to capture every step as I went through it.
The starting point is here: http://copyright.gov/eco/
Up to 8 months later (yes, it really can take that long, since the Copyright Office processes over 600,000 applications per year), you will receive your official certificate. But don't worry: the copyright date is considered to be the day you fulfilled all the requirement of the application.