Not necessarily. Maybe the scanners have a key that only it's creators can derive from some master key. The hash could come signed and all the public verification has to do is match against a public key. You don't need a database of hashes and you don't need a centralized db of source scans. Each scan hash could even chain with a previous scan hash and you can limit the number of times a key is good for, hence limiting number of scans a device can have. Only way to fake this would be to have the master key.

Which, as always, raises the question of why a blockchain is necessary. If the creators' master key can be trusted with the power to decide who gets new coins, why don't the creators just store everyone's account balance in a database, and get rid of the enormous performance and energy costs of a distributed ledger?

> raises the question of why a blockchain is necessary

For marketing, of course. Blockchains are magic, the rubes won't flock otherwise.

I don't know anything about Worldcoin specifically, but you could argue a case for an initial period of semi-centralized "fair" distribution, after which the protocol would (verifiably) cease to allow minting of new coins.

Exactly!