Do you want to prevent photos from being stolen or concerned about other websites stealing your photos without crediting , you might want to try watermarking your images.
You can add watermarks to your images either online or using an software on your PC. If you want the online option, here are the 2 Ways To Watermark Your Images Online.
If you want the software to Watermark you images here it is
Free Watermarking Software
Checkout these List of Digital Photo Watermark Software which you have to pay (not free).
(Removign this link as it is not a active site) WatermarkLib – WatermarkLib is a free watermark software that lets you to create watermarks out of graphics and text. It helps to protect your photos & digital images from unauthorized uses. Batch Photo Watermarking feature gives you many options to retrieve photos from a folder, and add watermark to each picture in the folder in seconds. You can easily add date and time on the memorable digital photos with Watermark software.