Do you want to prevent photos from being stolen or concerned about other websites stealing your photos without crediting you, , 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 few great tool that does the job easily.
Free Online Watermarking Websites
Watermark your photos online!
PicMarkr – PicMarkr lets you to add custom watermark (image or text) to your images online very easily . You can upload images from your PC or you can from Flickr.
watermark.ws – watermark.ws is an another great online watermarking tool which offers features like batch processing, resizing, image compression, text and image watermarking with transparency and organizing your photos just to name a few. No download. No installation!