Piece by puzzle piece, Fla. county checks suspects' identities
When prisoners first enter the Pinellas County, Fla., jail, a facial recognition system shows immediately whether they've been there before.
Each year, about 50,000 prisoners come through the doors of the 3,100-bed Pinellas County Jail in Clearwater, Fla.
'We get everybody who is arrested in the county,' said Lt. James Main of the Pinellas County Sheriff's Department. 'The number has been increasing over the years.'
Identifying prisoners as they come and go, and come again, turned into a puzzle for corrections officials.
'We know that about 65 percent have been here before,' Main said, although they don't always give the same name.
The department has kept a digital fingerprint file since 1995, 'but if you get an uncooperative person, you can't take fingerprints right away,' he said.
In 2001, when a 7-year-old proprietary mug shot system was due for replacement, officials decided to try facial recognition technology to identify prisoners at booking. 'We were doing facial recognition for years before we got the software,' said Main, who has been booking prisoners for most of his 16 years in the department. Individual officers would try to remember if they had seen a subject before.
The new recognition system from Viisage Technology Inc. of Billerica, Mass., searches a database of 550,000 digital images in a matter of seconds for possible matches with a new prisoner's face. It does not replace fingerprints, however. 'We call it preliminary identification,' Main said. 'It's a good complement to fingerprints.'
The department wound up playing an active role in the product's development. 'We thought we were buying a finished product,' Main said. 'But when we got into it, we found it was an evolving technology.' The sheriff's department became something of a guinea pig.
Deployment began in the spring of 2002, said Viisage chief technology officer Mohammed Lazzouni, and 'it grew as the need of the customer grew.'
Images are captured by PC software controlling a kiosk-mounted digital camera that snaps a picture as a prisoner enters the jail. The software automatically finds the subject's face in the field, centers and focuses on it, and checks the resulting image quality.
At the back end, Viisage FaceExplorer software on a rack-mounted server searches a customized Oracle image database for matches.
Although the Viisage system is essentially software, it requires so much customization that the company usually installs it on hardware for each customer.
Even without the face-matching function, the kiosk was an improvement over the old mug shot system, Main said.
'The way we did photos was very subjective,' he said. As many as 10 pictures might be shot before one satisfied the photographer.
Now the Viisage system enrolls each digital image and makes a numeric template of it. The Viisage system at first used a facial recognition technique called independent component analysis. 'When we had squeezed it as much as we could, all we could get out of it was accuracy of 65 percent to 68 percent,' Lazzouni said. So the company added a technique called elastic graph matching for similarities. 'We now have an accuracy rate in the neighborhood of 91 to 93 percent,' he said.
That does not mean the system is wrong 7 percent of the time, however. The final determination is up to a human being.
The Viisage system turns out a gallery of possible matches rather than doing a one-to-one comparison. The user determines how many matches to return.
Pinellas County chose to have the top 50 matches returned, tightly grouped at the top of the photo gallery. Because so many prisoners are repeat offenders, the matches often are multiple pictures of the same person. A booking officer inspects the gallery and makes the identification.
Pinellas County has enrolled its digital mug shot archives dating back to 1994, and Main said the software can find matches that might not be obvious to the naked eye. Beards and shadows have little effect on matching, he said.Other counties linked
Each prisoner receives a photo ID card, which is compared with another photo taken at the time of release to ensure that the right prisoner is getting out of jail.
The department's investigators can query the database from their computers. Several surrounding counties also have established links for searching across multiple databases.
The sheriff's department is now replacing dumb terminals in its 550 marked patrol cars with Dell Inc. notebook PCs equipped with 1xRTT wireless network cards. Fifty of the cars will get the Viisage system with a digital camera that can be docked to a notebook PC running FaceAlert.
The software enrolls a digital image and sends it via a virtual private network to the FaceExplorer server. The officer in the patrol car then sees a gallery of possible matches on the notebook screen.
The first officers to use the mobile system will be in traffic enforcement, Main said, because they pull over the most people.