Haven't received postage mail regarding pictures, but I have received emails that said:-
1. Congrats! your pic has been chosen for our upcoming book...
2. We are a web stock agency and found your photo at abc.com and would like to represent you...
3. Earn $$$ with your pics if you agree to let us market your photos...
And the standard response is ... DELETE! DELETE! DELETE!
Another thing to watch out for is Photo Competitions where the competition organiser requires you to hand over ALL RIGHTS to the photo to them (doesn't matter if win or not - the moment you pass the photo to them, it belongs to the organiser and they can do whatever they want with it).