Dupe n scale

Building off of hints from other posts, I’m trying to see how to make a photo gallery (thumbnails & picts) in ActionScript. Basically, the “thumbnail” is a scaled down version of the actual big pict. Clicking this thumbnail duplicates itself, then enlarges to full size next to the thumbnail list. The thumbnail then goes to alpha 50 to indicate that it has been clicked.
That’s how far I got with the attached sample (no actual photos for now, just colored squares).
My question is, how do I make the enlarged picts dissappear when clicking any other thumbnail? No matter what I try, they all stack up on each other. The photos I’ll eventually use will be different proportions, so parts of them will peek through, which is bad…