It works fine... for a single entry. When I have more than one entry on the page, the browser caches the first image it pulls and my "random" entry headers are all the same. I had planned to get around this by appending a random string of numbers (or I guess a timestamp would work) to the end of the image.
But durrrr, I forgot that LJ would disable any scripting! That just breaks the css. This is kind of a long shot, but does anyone know of a way to prevent the browser from caching an image... without using any prohibited scripts? I kinda doubt that it can be done, but I figured I'd try.