Have you a source for that? My experience of laptop webcams is that they need at least a second or two after power on to initialize the camera. That'd be pretty noticeable if you're using the machine, at least.
Specifically around the 18:00 mark. Also he does provide source examples that you can ruin your computer with if you want.
He gets into a lot of it, but shows quite a few examples including what I'm talking about. The people that he catches aren't necessarily savvy, but he does talk about taking pictures fast enough for the light not to be visible.
