You are a photographer on the internet, your images will get stolen - it's inevitable.
The issue is how much will you lose out from this?, and does getting your image(s) seen in the right place actually act as marketing!?
You can help prevent people from taking your images by doing various things. If you only distribute via microstock [2] agencies then you have some protection in doing so, they have already built-in all the legal and technical barriers there are to protect your images, but all this still won't guarantee to stop your images being abused.
Foolproof solutions to digital theft:
There is only one, don't upload any images, or sell any. In fact, better still, don't take any. It's a perfect solution, and the only one where nothing will get stolen... but you won't sell any images either. While you are at it, go bury your head in the sand too.
Even if you only upload to the main microstock sites, a quite secure approach; and one which is the only upload that lot of photographers do, there is nothing to stop someone paying for an image and then using it inappropriately. E.g. reselling it or using it against the terms it was sold under. While the stock libraries offer some legal protection and in some cases will fight on your behalf, you will have a difficult time proving which site the image was taken from if you are not an exclusive photographer with just one agency.
Protecting a portfolio site, sample images or a blog.
At some point you are going to want to create yourself an online portfolio [3], use examples in a blog post, or add some samples of your work for publicity on some sort of social network/photography website. Here are a few steps to follow to help protect 'Samples' if you choose the display them online somewhere other than one of the microstock agencies:-
Embed copyright into them using IPTC [4] copyright and author fields.
I had a case recently where I received an email from one of the smaller stock agencies I am not a member of, saying that someone was uploading my images, and they wanted to check it if it was me. They had read the IPTC data I had embedded into the image and found the URL of the website where I provide some of my lower quality work for free (for self promotion [5]). The upshot of this was that they let the user in question know that it was not acceptable to try to sell images belonging to someone else. There is nothing to stop someone removing or replacing your IPTC data, and no guarantee that someone will actually take the time to look at it, The agency involved thanked me for marking the images, it makes their life easier, also mentioning that a lot of people don't embed such data!
Watermark the images.
Either manually in photoshop or set-up an automatic watermark facility in the site you are using if you can. Include your name, copyright and url so that people can contact you if they have one of your samples, or find them re-posted on a different site even if you did not give permission for that to happen. Watermarks are no guarantee; unless you obliterate most of the image with your watermark it's still possible to crop or clone out a watermark. Watermarking is a deterrent for casual photography thieves.
Only provide lower resolution versions.
The higher the resolution the more use the image is. Make people pay for that valuable hi-res version. Getting a watermarked, low resolution version of your image online for potential buyers to see is one of the best marketing tips I can give to a microstock photographer.
Right mouse button protection really is not worth the effort.
(activate it if it is simple for you, but don't spend too much time getting something working), it can easily be defeated by print screen on the PC or dragging the image to the desktop. It will annoy genuine image users from downloading a watermarked comp [6] image or stopping them from emailing to a colleague for approval etc. (having your image on their system with your watermarked contact details on it is the best 'bookmark' you ever get!).
Always: prominently display contact information and a copyright policy with every image you display, email, or sell (if you only use the microstock sites then they handle this for you).
You can help search for images that might have been stolen using the tineye image search [7] but only if it is in use online. Also, If you have the image uploaded to a microstock site then only if you have made no sales can you tell if the image has been stolen.
My advice would be not to spend too much time hunting for stolen images, or trying to get just one of your images removed from a foreign language website. It's a different story if you find your whole portfolio ripped off then you have a duty to sort that out, the person who stole those images has probably stolen from others. Focus on the things that are important like friends, family and life; not an obsessive battle over the use of a single image which you are unlikely to win unless all your friends are lawyers.