Servers are usually computers with really big hard drives that are always connected to the internet and allow people to look at the files they contain. The computer that holds all the files that make up my webpage is a server, for example. If your own home computer acted as a home for a webpage or RPG and let users in other locations look at or interact with the files on it, it too would be server.

Basically, you need one of these things to house the pictures. Geocities and Angelfire are places that also have servers that host webpages and picures and things. There are also places that let you just put up photos online. You could use any of those if your school didn't provide you with server space as MIT does.