I also make use of PNGs (this is old news though) so I can swap out my background image easily.
I can’t take credit for the workings of the POP-ups though, this is all down to Highslide JS. Highslide was great for usability but not so for Google Analytics. I won’t bore you with the details here but I struggled to get the onClick tracking for the thumbnails. So have resorted to using onmouseup to track clicks and onclick to launch the POP-ups. It’s not ideal as I still need to work out how to track when someone uses the left / right controlls. But the way it’s set up now I can tell that the image I’ve used at the top of this post is the most popular.
Next step, get random background images to load up behind the thumbnails.