In the US there is a system of “registering your copyright”. It does not mean that you have to register to be the owner of the copyright of the images / photographs that you do. But it does mean that it will be much easier to defend your rights if someone infringes on your copyright and steals your images, if you have them registered. It also means that you can get much higher damages awarded by a court.
It explains how to register you pictures using the Electronic Copyright Office System, eCO, by the US copyright and patent office.
The post is from 2008 but still very useful.
Do you register your copyright?