13 July 2005

Do they "sort of" torture you once they've arrested you?


In its continuing search for a technological "silver bullet" that will eliminate the threat of terrorism, the intelligence community has turned to face recognition.

Now, given that my own particular face recognition abilities regularly let me down, maybe I'm overly skeptical of this. But as far as I know, there isn't even software that can recognize the letter "A" in all the cases where humans can.

Luckily, the maker of this system is managing expectations:
"It does a reasonable job of matching people that sort of look alike," Pixlogic chief executive officer Joseph Santucci said. "Most [competing] software tools only work under constrained circumstances."
Designers of alarm systems like this face two competing problems, known as Type I and Type II errors. A Type I error is one where the thing to be detected exists, but isn't detected. In this case, the Type I error is where it fails to match a terrorist to his picture. Type II errors are the converse; the thing doesn't exist, but the alarm goes off anyway. When you're walking around and are mistakenly picked up as a terrorist because this system said you looked like one, that's a Type II error.

There's a tradeoff between the two types of errors. If you want one type to happpen rarely, the other type will happen more often. And both types are big problems. Not identifying a known terrorist who then goes on to kill is one; but a system that causes police to arrest many innocent people can lead to a tendency to ignore those identifications, just as no one pays attention to car alarms anymore.

Any guesses as to what balance they will strike on the two error types?