This clever ad was posted in bus stations around Hamburg, Germany. When you look at it you’ll see a couple smiling. When you take your eyes off it the image will change and the man will beat the woman. “It Happens When Nobody Is Watching” is the slogan of this Amnesty International domestic violence campaign.

So how does it all work? Well it looks like the poster has an eye-tracking camera which can trigger the image switch. That’s a pretty interesting use of current technology in order to deliver the right message. If you’re in Hamburg better bring a friend to properly watch the whole picture change. After all, how many pairs of eyes can the camera follow?

via copyranter