if you happen to know their search terms, you'd have the answer.
if it's type in traffic, you can always post a poll as in.
"Dear User, thanks for visiting, we don't really know what we should serve you with. Why don't YOU tell us what you want to see on here" Then place either a poll where they just hit a button and DON'T have to register to vote, for which you get a pretty good idea as to what they're looking for. OR, since you already pointed towards image hosting, see whether there are affiliate programs out there where you can just simply link to other sites. make some cash as a referrer. again, make sure it looks decent or no one will click the links.
last but not least, if you wanna go and develop, you'd still be best off with an image hosting site, with 40k traffic you have enough reason to get that started. just make sure you're making a bit of a difference and don't look like all the other image hosting sites.
Edit: I just read in your other post that you know what 100% of your traffic is looking for. There shouldn't really be a problem/question then. Check with your attorney regarding copyright violations and how you can distance yourself from these if you're running an upload/image hosting service and you're ready to go.