It would be pretty hard for the attacker to precisely arrange a hundred tiny sprinkles on the surface of a pill to exactly match a known-good pattern. (At least compared to just throwing a bunch of assorted sprinkles on the pill randomly and taking a photo of the result, which is what legitimate manufacturers would be doing.)

yeah, this is one common claim about sprinkles - that the pattern can't be reproduced. Is that so true? Manually, sure, probably, perhaps. But if sprinkles signing is common enough, or the attacker has enough budget - and they do - then sprinkles matching deserves a machine. A sprinkles printer.

And if you have a standard algorithm which converts a sprinkles picture or three into a hash. Then now you have a precise target for the machine to benchmark against.

I guess this would be easy to spot for the end user. Maybe the app that is used for checking the pills can alert the user if one pattern is scanned multiple times.

Showing how often an authenticity code has been checked is something manufacturers like Xiaomi do, where there's rampant counterfeiting.