Not sure if you say, but Kaoz mentioned it first, I agreed with him, and I say it is a scam, no one can offer unlimited.
I disagree with everyone here saying you need a VPS or dedicated server (unless you reach the point where you absolutely need the upgrade), I do however agree that one should avoid oversellers. Image hosting is not as resource intensive (CPU/RAM) as you think, only thing you have to worry about is bandwidth for the most part because people will be hotlinking. Most hosts allow adult content, and most will also allow monthly payments so you can give it a test and see if it suits your needs, but do check the hosts terms of service to make sure they allow it.
I have to add that image web hosting is a separate class of web hosting and you have to remember about it and understand it. Just give google a try and I'm sure that you will find plenty of. Good luck
Many thanks for you input on the special hosting requirements i am going to go down the route of a vps host and as we grow the site we will then look at a dedicated server.One question is if i decided to add another Adult image site would i need another vps host or can i add this to the 1st vps one if that makes sense ???? We should be going live with the new site by the middle of next week while we tweak the site and this is currently sitting on a normal host but with no images on it at the moment.Thanks