办事指南

Triumph of the old

点击量:   时间:2017-05-16 06:02:09

By Phil Cohen San Francisco OLD-FASHIONED film cameras are better at catching bank robbers than modern video cameras, according to an FBI report presented at the American Academy of Forensic Sciences. Bureau scientists say video cameras can be useless for identifying criminals. In the early days of surveillance, banks had hidden film cameras that were triggered by staff during a crime and snapped photos every few seconds. But in the 1970s, many banks switched to video cameras, believing that it was important to be able to monitor an area continuously—and to cut the cost of using film. Now most banks use video. “We’re seeing so much more video than we do film,” says Thomas Musheno, a forensic scientist at the FBI laboratory in Washington DC. The problem, he explains, is that the FBI usually uses tiny details they call “unique identifying characteristics”, such as scars or moles, to identify a criminal. In close-up, video can capture these features as well as film. But cameras are often mounted 6 metres from tellers. At that distance, an image of a gunman’s face can be decidedly uninformative. “You can hardly tell it’s human,” says Musheno. The cameras normally record a picture field once a second—making a 2-hour tape last for 72 hours. Only every second line of the 480 lines on the screen is recorded in each field. So if a distinctive wart or scar lies in the odd lines,