Curiousity kills the cat and me and my mother always said I asked too many questions!

So here is another as I learn about this universe...when Istockphoto and Shutterstock claim to have 1.2 million images, does this mean 1.2 million unique images or # of downloadables? so 1 image may have 3 downloadables so really 400K images? I ask because it would seem to me that the less number of images the better the chances of getting seen and purchased?

Any ideas?