system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: if everything is registered in computers and databases, why do fake passports still work? Should they fail on arrival when read thru the machine? Like a 404?
gpt
Because as example the US customs does not have access to the "British citizen passport database". The data on the passport is the same as the written one, including error correction keys and nowadays some biological data as well (such as fingerprint). It also depend on the issuing country and how old your passport is.

All they can do is check that it's correct and matches you as a person. And cross reference with their own data of persons denied entry etc.

TL;DR; there is no secret world wide database with everyone's information for them to connect to.