A while back, I shared how you can use cellophane tape to keep people from spying on you with your webcam.
For the past month or so, I've been using an alternative called the SpiShutter which I really like so I wanted to share it with you. Here is a brief video walk-through showing how it works:
I have the black version of the SpiShutter, but they come in a couple of other colors, as well.
By the way - the privacy screen I mention is the 3M Gold Privacy Filter for MacBook Pro Retina computers - they are available for most other computers, as well. That's meant for a different kind of privacy - namely, to combat shoulder surfers and neighboring travelers - and I swear by them. [Updated - corrected broken link]