Well, the description of how the system works, in the article, makes it sound like it has a database of passport photos for US citizens, and a database of photos taken on entering the country for citizens of other countries:
>> The new veriScan system developed by the Metropolitan Washington Airports Authority—with guidance from U.S. Customs and Border Protection—scans the faces of travelers approaching the gate. The system then compares the photo to a gallery that includes images of that person—either their passport photo for U.S. citizens or the photo taken of foreign nationals when they entered the country.
So that's definitely not just the passports that have been checked into the flight- foreign nationals in particular may have entered the country at any time and place other than before boarding a flight at Dulles.
Which is why there are privacy concerns in the first place- because it can be used to track the movment of people across multiple trips.
>> The new veriScan system developed by the Metropolitan Washington Airports Authority—with guidance from U.S. Customs and Border Protection—scans the faces of travelers approaching the gate. The system then compares the photo to a gallery that includes images of that person—either their passport photo for U.S. citizens or the photo taken of foreign nationals when they entered the country.
So that's definitely not just the passports that have been checked into the flight- foreign nationals in particular may have entered the country at any time and place other than before boarding a flight at Dulles.
Which is why there are privacy concerns in the first place- because it can be used to track the movment of people across multiple trips.