[logfromblammo]

In order to establish a "one account per human" rule, I think using some form of biometric identifier will be inevitable.

My first attempt would probably be a 600 DPI flatbed scan of both hands, palms down, with a nonce written on them with a marker. But since I am a stinker, the nonce would be a procedurally generated phrase similar to "22Feb2017 @randomhandle 03D6A9C1 #RateMyHands", and my trust would wither in the ensuing user data privacy scandal.

I'm sure someone more mature and responsible than I am could do better with that idea.

If you can determine that a new account has the same hands as an existing account, you can stop depositing into the old one, and continue with the new one. You can start with human eyeball inspection, and work your way up to automated hashes of extracted features.