Photo and Art Stock Internet Sites - Good Profitability?

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I am keen to know if anyone here has tried selling photos/artwork at the popular internet stock sites (e.g. Big Stock Photo) and made money. What type of photos/art sold the best? Were they customized/edited? Was one site better than another and why? Is there a particular category (e.g. people, buildings, etc) that sells or is popular? I'm looking for a good featured site to sell some of my photo's and computer generated artwork...