In order to crack down on the number of immigrants who stay in the U.S. illegally on expired visas, the federal government is making some foreigners undergo facial and eye scans when they enter the U.S.

According to a 2006 study by Pew Hispanic Center, about 40 to 50 percent of people in the country illegally are here because they overstayed their visas. As a result, authorities have no way to identify them due to the absence of a checkout system.

To change that, officials launched an ambitious effort to track people who enter the country on visas. Starting on Thursday, the U.S. Customs and Border Protection began a pilot program that captures information about foreigners entering the country at San Diego's Otay Mesa port of entry on foot. By February, the program will be expanded to foreigners walking into Mexico through the checkpoint, reports The Associated Press.

The trial will run through June. Authorities will then determine if eye and facial screenings should be expanded to foreigners at all crossing on the U.S.-Mexico border.

"It's very fast, not inconvenient in the least," said Rosendo Hernandez of Tijuana about the screening process, which reportedly takes less than a minute.

Officials say the scanners read chip-enabled travel documents at a distance and match the information to entry records.

"It's basically to verify that the same person that came to the United States is the same person that's exiting the United States," said Joe Misenhelter, assistant director at Otay Mesa.

"We have historically controlled our borders coming in but not out," said Jim Williams, a former Department of Homeland Security official. "It's been a lack of infrastructure and lack of investment."

Marc Rosenblum, deputy director for U.S. immigration policy at the Migration Policy Institute, applauded the effort, saying it to fix "the biggest deficiency in the whole system."

He added that, "It's a huge deal. What they likely hope is this could be a fast exit check that won't be terribly expensive or time-consuming to implement."