Totally different concept, but this reminds me of the anecdotes my professor would tell us about the possibility of eavesdropping on a monitor (CRT then) based on the light radiation emitted, and not from seeing the actual image itself
You're thinking of Optical Time-Domain Eavesdropping Risks of CRT Displays by Markus G. Kuhn in Proceedings of the 2002 IEEE Symposium on Security and Privacy, Berkeley, California, 12–15 May 2002.
Pretty amazing that this actually works, just using a high-speed photo-sensor – and doesn't even require line of sight, a reflection off a wall is enough. Unfortunately, I don't think it will work on LCD screens.
