This isn't even multiple layers of a photo. It's one static photo, wrapped around a very simple convex mesh. The eyes (bloodshot as hell) and mouth were then faked to make them movable. The lips are probably real, sure, but look at her teeth. They're flat gray. No shading. No texture. They're evenly spaced apart, despite that nobody's teeth are that evenly spaced, especially when viewed directly from the front. And when she smiles, the lips maintain their exact form and shape. The creases in the lip do not tighten. Basically the various parts of the mouth just deform away from each other to briefly reveal the photoshopped teeth.

I'd point out what's wrong with the eyes but Clarice already nailed that.

There's other bits too. There's no depth beneath her chin where it juts forward away from the neck. There's a shadow there, sure, but look how it changes (or doesn't) when you move the mouse up and down. It just deforms, the chin doesn't actually move down in front of it.

Okay, so I'm going to stop here. I think I've nitpicked it enough. It's an interesting effect, and creepy, and it got a 'woah!' out of me before the initial impact subsided and all I could see was its flaws. What I'd like to see is a veteran game programmer create the same thing, like maybe some of the people that put Half Life 2 together. That would be amazing.