This is attributed to Justin Oberman, a former senior official at the Transportation Security Administration
That passport scan transmits the information to Customs which it needs to perform watch list matching for international flights. Currently, there is nothing analogous in the domestic market. The reason that’s a big deal is because the carrier’s last choice is to be required to collect this information during the reservations process. That remains a major hurdle.
and from another story about it where they had an immigration officer demonstrate what visitors from outside the US went through:
Quickly, firmly and yes, politely, an Immigration Officer welcomed this reporter by capturing her "biometric information" in a two-minute exchange.
She asked for my passport and entry document
She swiped the passport through a barcode reader
She told me where to place each index finger on a box-like camera
She asked me to pose for a digital photo
For the purposes of this demonstration, we were shown the results on a flat screen monitor. A passport scan reveals several details or "hits" that might alert an officer to order a secondary screening of the visa applicant. Additionally, the biometric information (digital fingerprint scans -- barely readable to this reporter -- and photo) are checked against various government databases and Watch Lists to turn up matches, either to verify the visa holder's identity or find "those who would do us harm," as US government representatives noted in a panel discussion afterwards.