This scientific paper was published two years ago, but I missed it. It may be an oldie, but it's a goodie. Computer scientist Markus Kuhn demonstrated a way to read CRT computer monitors at a distance using a photosensor, even if you're not facing the screen.
An image is created on the CRT surface by varying the electron beam intensity for each pixel. The room in which the CRT is located is partially illuminated by the pixels. As a result, the light in the room becomes a measure for the electron beam current. In particular, there is a little invisible ultrafast flash each time the electron beam refreshes a bright pixel that is surrounded by dark pixels on its left and right.
So if you measure the brightness of a wall in this room with a very fast photosensor, and feed the result in another monitor that receives the exact same synchronization signals for steering its electron beam, you get to see an image like this (after using a mathematical signal processing technique–ed.)
