It's a tough one.
From past experience, realistic looking chops get posted around so much that they eventually find their way into 'stock' photos. In other words, it gets reposted, someone somewhere removes your name and modifies contrast etc, uploads it to a wallpaper site, and as a result it gets shared all over the net.
From there it is very hard to trace the rightful owner, and often ends up being posted in "free to use" web directories, meaning that the magazine may not have knowingly done anything wrong. They may even have gone to one of these stock sites in good faith, taking it without realising. The fact is that today it is very hard to protect your work.
The key thing to remember is:
-In most cases there is no ill intent, and it may even have been a mistake
-Treat things sensitively, it's better to be polite and courteous - you're much more likely to get a civilised response. In other words, just a gentle message to the magazine explaining your circumstances and that you put a lot of effort into the piece, and you would appreciate it if they sought permission in future - don't go straight in demanding money, wait for a response then maybe see if you can negotiate something.
Could you possibly post the magazine shot in higher resolution, I might stand a better chance of working out where it's from then
