http://www.dpreview.com/articles/309428 ... regrets-it
This is the original aricle to which DPReview links and it is worth reading for anyone who regularly posts to photo sharing sites or has a website for their photography. It does raise the question whether those who have an image appropriated on the web should be unduly concerned given that the people who do it have no conscience and/or awareness, and there is no commercial value in their dubious activities. It's another matter entirely if someone is seeking financial gain from using the image. As for trolls and cretinous web vigilantes, that's only likely to be an issue if an image receives widespread recognition. I'll take my chances.
http://petapixel.com/2014/07/25/things- ... nt-posted/
Personally, I usually just post nothing more than a relatively small, low resolution JPEG online. It's not ideal, but it limits the potential for misuse by others.