I still remember, from at least twenty years ago, an anti-duplication technology based on this idea. IIRC it involved embedding glitter in clear plastic and then measuring the reflections at different angles. Devilishly hard to duplicate, especially since one wouldn't know which angles would be used in a reading so the placement would have to be nearly perfect in every dimension. Unfortunately so would the alignment in a reader, which I think is what sank the idea. Still, the idea of physically embodying something so similar to a mathematical proof of work seems valid and quite appealing. "I could never in a million years make the glitter fall that way again."

P.S. Here's a modern application of a similar technique to detect tampering with a laptop. https://archive.ph/g1kDW