The best way to mark up images for SEO?

The members of the Cre8asite forums are currently debating the best way to name images for SEO purposes with some interesting theories surfacing. From personal experience I noticed that one of my clients’ sites started to rank higher for British international motor show (and other shows) once I labelled their images with the names of the shows in their alt elements. If the images were also called “british-motorshow-honda-1.jpg” for example I’m sure they’d rank higher too. Something I’ll incorporate into the new version of the site I think…