not sure if this is what you want but why not run a normal ftp server and connect to it from IE or firefox, then drag and drop into the window.
it gives you simmilar resaults however i am not sure about the multifile upload, i dont think that you can do that or at least easily
it sounds to mue like you want a generic file upload interface for pictures and want to do it with an ftp backend (because it allows uploads) however what you describe is in fact somthing else (ethier webDAV or a php script on the server dumping the data)
a webdav server wolud be nice and would work but would most likly create extra effort, if the issue is ease of use then i would go with teh IE/firefox idea. if its a long term solution then map the server (over webDAV or ftp) as a drive under windows or linux so it appears local to them
I forgot to mention that. I do have a "normal" ftp server running. I really am just looking for the front end interface.
Maybe mapping the drive via samba over ssh may be the way to go. Hrmm....