They use both. They crosscheck you against stored biometric data from the passport, and also the data stored in the passport against data previously seen. If s

They use both. They crosscheck you against stored biometric data from the passport, and also the data stored in the passport against data previously seen. If something is not matching they put additional scrutiny on you. It is not perfect. Super spies, and determined smart criminals are going to be able to defeat it, but it raises the bar.