Well, it seems like this people are not really running a scam on you but making big bucks from explioting your talents.
If you guys don't know, stock images are the biggest income earner in the media business but if you are not aware, you guys can get suckered by selling your rights to a good pix to be used in big adverts or broadcast for millions while you get a few hundred bucks. Go check out places like Asia Images, Photolibrary, Gettys Images (big timers locally & internationally). Ask for their rate cards for usage and see how much they are getting from the users and what do the photographers get. Even National Geographics make most of their income from such image rights usage but their photogrpahers are still well paid.