i have gone into the cpm & affiliate route with my imagehosting site, though not much success yet. I would guess its more to do with type of ads than placement.
1) where are you getting the traffic? 2) what does the page design look like? 3) do the pages have a theme, or a consistent subject matter?
Switch to file hosting. This way you can still provide image hosting and get more broader audience. Watch and learned how other file hosting place their download link blended with adsense ads which I'm sure make more than what you get right now.
traffic is 40 % from US and rest from all over world. Page design is simple and i didn't test it much. But just to let everyone know, Auctionads made me $ 12 in 2 days.