Computer systems is what is on the horizon.
snip
A top official at the Department of Homeland Security says the agency will start
deploying a long-delayed computer system in 2018 to detect when foreign visitors
and temporary workers fail to depart the United States on time.
Technology is really advancing, to address visa overstays.
The biometric system being tested now (and will be rolled out over 2018) will capture photos. The ability of Artificial Intelligence applications to recognize faces is now (just recently) better than humans.
Law enforcement systems could soon link up with a variety of cameras (like at toll booths, maybe ATMs, even iPhones), to enable constant automated searching for the faces of visa overstays. China is probably ahead of us on this right now, but they have done it by hiring Western companies to develop it.