BTW, webwit has enabled SVG support in MediaWiki now, which means that graphics can be uploaded in vector format now. This brings graphics in line with the spirit of a wiki.
For those who don't know vector graphics, think of it as open source graphics – the source of the image is the image: every line, circle, label remains editable as its own object, and you can clone objects such that when you alter one of them, all the clones update automatically. This means that you can save an image from the wiki to disc, tweak a line or circle or colour or edit a caption, and upload a new version really easily. It's also infinitely scalable, unlike a PNG or GIF that becomes pixellated when you enlarge it.
Inkscape (which I use) is a pretty reasonable FOSS SVG editor — no-where near as buggy or crashy as it used to be in the past ;-) (apparently the Windows version was far less stable than the Linux version, perhaps due to GTK+ bugs under Windows).