According to the Associated Press, which first reported the plan on Wednesday, facial-scanning pilot programs are already underway at six American airports—Boston, Chicago, Houston, Atlanta, New York City, and Washington DC.
In a recent privacy assessment, DHS noted that the "only way for an individual to ensure he or she is not subject to collection of biometric information when traveling internationally is to refrain from traveling." In recent years, facial recognition has become more common amongst federal and local law enforcement: a 2016 Georgetown study found that half of adult Americans are already in such biometric databases.
But he also said that the agency may keep scans longer after it goes "through the appropriate privacy reviews and approvals." US Citizens are not exempted from this process for two reasons: first, it is not feasible to require airlines to have two separate boarding processes for US citizens and non-US citizens, and second, to ensure US citizen travelers are the true bearer of the passport they are presenting for travel.
If the photograph captured at boarding is matched to a US citizen passport, the photograph is discarded after a short period of time.
"We've determined that it's OK to treat Americans differently on entry, why is it not OK to treat them differently on exit?"