You're pretty much reinventing the wheel. If you put a watermark in your images. How are you going to find the individual who is plagiarizing them? It's a big interenet out there. My suggestion is to use Digimarc
's service which you can use Photoshop to put watermarks in your images and let Digimarc
look for those who are infringing on your intellectual property while giving you more time to create more images and maintain your site. Digimarc
's spider goes out to look for images that are your property and if they are not on your site it will let you know. If your images are your bread and butter then I think it would be well worth the price.