Catching parking scofflaws in San Francisco has become easier with the help of high-tech cameras that scan license plates in search of cars saddled with unpaid citations. A city parking crew operating the new system can almost instantaneously find cars with at least five outstanding tickets. A two-person team roams city streets with two small cameras mounted atop their unmarked vehicle. The cameras can scan 250 or more plates an hour. And when a match is made, the crew attaches a yellow metal boot to the front wheel, removing it only after the tickets are paid. The city's Department of...