I remember Elite on the ZX Spectrum had a novel scheme : a prism that you held up to the screen after loading the game to read a challenge code. Quite effective in that manufacturing a similar bit of plastic was beyond the ken of most teenagers.

Here's the wikipedia page : https://en.wikipedia.org/wiki/Lenslok

Seems to me that modern displays know how big and high res they are so could calibrate the challenge to the lens lock size, so perhaps this brand of weirdness will ride again!