I don’t think most cloud services will work. Basically, if the service doesn’t maintain the folder structure, it won’t work, as the images are referenced strictly by that structure (and most simple hosting services don’t maintain that structure).
I think dashingdon’s hosting (or a direct link to his site) allows image uploading (and is dedicated to CS games). Outside of that, Webs.com was what I first used, and it still works (although there’s a week wait before registering and uploading).