My manager at my last job actually did this to one of his good friends many years ago after I showed this article to him - whenever the friend was using my manager's WiFi any images would be upside down, or blurred etc etc. He took great delight in telling me that the friend had even reinstalled his OS to try and solve it.

A couple of years later, said friend actually joined the company. I used to take great delight in dropping occasional obscure hints and comments, but he never did figure it out.