I was immediately reminded of the Dual Photography paper (well, I had to look it up first; I only remembered the "photographing a playing card that is facing away" demo at the end):
That's an absolutely science-fiction-esque paper. I can't believe that's real, and I'm surprised to see such little follow-up research. I assume it's not practical to generate the light transport data with any reasonable speed?
- http://graphics.stanford.edu/papers/dual_photography/
- https://youtu.be/p5_tpq5ejFQ