I need some HTML help

Hey folks, I need some advice. I'm writing up a photo gallery for Barrel's website, and I have a nice setup with thumbnails that open in new windows. Now, I want to make it so the popped-up windows are only as big as the pictures.

I did some looking around, and all the ways I found to do it have been using JavaScript. I want to keep the site as simple as I can, and although JavaScript is fairly standard these days, I'd rather do it in pure HTML. Google didn't give me any indication that it can be done, but I'm hoping there will be a way.

If it's mind-bendingly obvious, then we'll all share a laugh about it.