Arbor.js is a great little library that lets you make visual thesaurus style springy node diagrams using JSON network descriptions. I worked on a visual intro for a client, and while it wasn't right for them in the end I had fun playing with the library. A lot of the power of this comes from the renderer.js file, which essentially allows you to write your own functions for outputting the data. In this case, I added a method to allow images to be used. It is, however, fairly badly documented and you'll have to work out a lot from the examples.
This has in no way been performance tweaked, doesn't run on IE and crawls on a tablet. Also you may need to refresh a few times to get the images to load properly. I know, it's basically perfect right?
Documentation aside it's a very elegant, easy to use library and I'd definitely consider it for other projects.
Thanks to the folk at ION.