Hi RichBrew,
Lucky coincidence there that you were able to catch the git red handed. I suppose its the unwritten Terms and Conditions of posting on the internet that some bastard will always try to rip you off no matter what you do. I add small watermarks now but they are very easy to remove or crop out, my site has loads of security features but there's a very simple way around them all.
The only alternative is not to post them at all as you have done. I dont think thats a solution I want to be forced into by the rip off merchants, I would never have discovered such fantastic sites had it not been for the photos on Megalithomania and Irishmegaliths and I think the more documentation available the better. Words dont really do many of them justice, they really need to be seen to be appreciated. In the end, the more interest that is taken, the more likely the monuments will continue to be visited and hopefully taken care of, cleared of brambles etc.
It would be a huge pity if photos of the less well known sites were taken off the internet, most would probably fall off the radar completly and less and less people will know about them and more importantly appreciate them. At the moment I think the incidents like yours may well be the price that has to be paid to keep interest in the monuments alive and growing, hopefully by showing the sites as best I can on the net I'm helping out in a small way. In the meantime we all have to be vigilant of the rip-off merchants, I might add contact info to the posts here so at least they know where to ask. Maybe you could re-post smaller versions of your photos that wouldn't be of much use to publishers?