Well, whether you post to pic sharing sites (or here!) or not, the copyright remains with the photographer and what this seller is doing is theft, pure and simple. You can get lots of info on copywright issues from places such as photographers direct etc.
However, if your images are in there, the seller is making a profit from your work and owes you a royalty payment, simple. Complain to ebay (mention that they are facilitating copyright theft) and also complain to AOL as he is using theor service for theft (you may like to emphesise this point to AOL). You could also contact the seller directly and ask for his IBAN (bank) details as if you wanted to make a payment, then contact his bank and again, inform them they are facilitating theft - the bank MUST then do something about it once notified, it's required of them by their regulators (even if the ignore it long term, they have to make an investigation which will be a PITA for the owner of the account!). If you have the equivilent of trading standards, complain to them as well and (if the seller is in the UK) you can sue him via moneydirect (HM Courts) even if your not resident in the UK (bit draconian I agree, but I've sued people over ebay stuff and won too!)
