Stop Unauthorized Use of Your Photos!
~reproduce the copyrighted work;
~ prepare derivative works based on the copyrighted work; and
~ distribute copies of the copyrighted work to the public by sale, rental or lending.
See 17 USC 106.
One of the ways infringers reproduce your image without permission is to "hotlink" to it. As defined by Wikipedia, hotlinking, (also known as inline linking, leeching, piggy-backing, direct linking, offsite image grabs and bandwidth theft) "is the use of a linked object, often an image, from one site into a web page belonging to a second site. The second site is said to have an inline link to the site where the object is located." While it's difficult to locate these infringements, you can find them by looking closely at your server logs.
Fortunately, there are ways to stop these unauthorized uses before they occur. Professional photographer, Walter Rowe, has a great article on how to Prevent Hotlinks To Your Images.
Also, Jackie Shumaker, a professional contruction and industrial photographer, has discovered how to remove your images from Google's image search. While you may want your photos included in Google's search for marketing purposes, there may be times when you need tighter control of them.
The Internet provides wonderful opportunities to display your photographs. Just make sure they show up where you want them to.