How does Flickr do this

http://www.flickr.com/photos/nukediver/110500052/

I've been asked by an acquaintance how to do this. I've taken a look at the source, and I can see that it's javascript, but it's also far beyond me -- possibly because it's created by Flickr's internal systems -- and it seems the style sheet is also involved. What I'm looking for is something he can work with fairly comfortably for his own site.

Any takers?

Thanks!