We've started to release parts of our source to the community. We're opening the doors with a parser function for MediaWiki...Imagelink.
Imagelink will allow you to make a link out of an internal image - to either an external URL or an internal page name. By default, MediaWiki will link images back to the Image page itself, rather than a URL. The common work-around is to use a #REDIRECT on the image page, but then you can only have an Image link to one URL and it has to be internal. This extension provides a method for linking the same image to multiple external or internal links.
We have to give a big thank you to Jim R. Wison for his work on this particular code and getting it ready for public use!
Learn more up at this projects Google Code page.