Easy to Make Money from your Photos

I have recently run across articles about how one can make money from their hobby of photography. There are so many students that take photos all the time and I wonder how many of them use some of these sites. After looking at a few (not creating accounts) I am not sure how one would decide which to choose.
iStockPhoto – One of the best known stock websites, although you have to reach certain criteria to be accepted.
Dreamstime - Must submit samples to be accepted.
Fotolia – Very popular with lots and lots of images.
Shutterstock - Sells subscriptions to customers so contributors make more money the more they upload.
This site has the four mentioned above plus others - 15 stock photography sites to see your photos

Maybe I should try this out....