The government's system for ensuring that foreign visitors leave the country when expected will be expanded to 11 more airports and two seaports, a Homeland Security Department official said Tuesday.

Asa Hutchinson (search), the undersecretary for border and transportation security, made the announcement at Chicago's O'Hare International Airport, which will begin participating later this month.

All foreign visitors who travel with a visa are fingerprinted and photographed, through the US-VISIT (searchprogram, when they arrive at major U.S. airports and seaports. The fingerprints and photos are automatically checked against databases to ensure that documents are legitimate and the visitor's name does not appear on terrorist or law enforcement watch lists.

Tracking the departure dates of foreign visitors has been a problem. An estimated 35 percent to 40 percent of undocumented immigrants have overstayed their visas, Homeland Security spokesman Bill Strassberger said.

The government has been testing an electronic exit system at Baltimore-Washington International Airport and Miami International Cruise Line Terminal. Visitors check out at kiosks, which electronically read documents, take fingerprints and a digital photo, and spit out a receipt verifying that the foreigner has checked out. Or, they can go through the same process with a US-VISIT staffer at departure gates.

The exit system will be added to these airports and seaports next month: William B. Hartsfield International Airport in Atlanta; Dallas-Fort Worth International Airport; Denver International Airport; Detroit Metropolitan Wayne County Airport; Newark International Airport, in New Jersey; Philadelphia International Airport; Phoenix Sky Harbor International Airport, in Arizona; San Francisco International Airport; San Luis Munoz Marin International Airport in San Juan, Puerto Rico; Seattle/Tacoma International Airport and the San Pedro and Long Beach seaports, in Los Angeles.

US-VISIT eventually is to be installed at land ports of entry. Next month, foreigners traveling with passports also will be required to use the exit system and supply fingerprints and photographs.