Facial Recognition Failed in Boston Bombing

From what I can tell, numerous people called in after the photos were released. Even if Thursday's events hadn't taken place, the police would have known the identities of both suspects shortly thereafter.

It just seems crazy to me not to acknowledge the role of investigators in all of this and chock it up to luck.

As for the edit you just made about the bombs in Hanover: are you implying there's a link to the Marathon bombers? Seems like conspiracy theory reaching - unless there's some sort of evidence you'd like to share.

Let's say that you want to catch terrorists creeping around in your airport. To do this, you have a magic camera that, when it takes a picture of a civilian, compares it to a picture of a known terrorist. If they're in fact the same person, it will flag security over. Let's say that it is indeed a magic camera and makes the correct decision 99.99% of the time, which is far better than the current state of the art[1].

Do you have any idea how much DHS or DoD would pay for such a magic camera?

But it won't be enough.

Consider a watch list of 100 terrorists that we're looking for in our airport. If our camera compares each civilian's picture to all 100 terrorists in succession, and if we model each comparison as a Bernoulli trial, then each civilian has a 0.9999^100 = 99.004% chance of getting through security unfazed, which means we flag innocent people as terrorists about 1% of the time.

This doesn't work in an airport setting. Assuming 5,000 people pass through your small airport per hour and you have a 14-hour day, that means your security people have to go through 0.01 * 5000 * 14 = 700 false alarms each day. That's about 1.2 false alarms per minute. Your security people will have to go through all their checks each time this happens. Before long, they're going to stop trusting your magic camera.

As you scale your watch list up, it gets worse. How well would it work for 1,000 people on the watch list? 10,000? Note that the current US watch list has 50,000 people on it.

Even if it were a perfect magic camera, it coudln't catch terrorists on their maiden crime who aren't on the watch list at all.

(Most of this post was adapted from: http://vast.uccs.edu/~tboult/tmp/IJCB11-tutorial-boult.ppt , which is a really interesting presentation if you're interested in these sorts of things.)

1: http://vis-www.cs.umass.edu/lfw/results.html

But then again, the police will label you as "that guy with weird bits of plastic on his face", which won't help you hide at all.

Costs $3, will beat any facial recognition

Think about it this way: would you want just anyone to be watchlisted based on tips that could be politically motivated, intentionally misleading, or just completely factually inaccurate?

What you can never account for in terrorism screening is the lone-wolf element. There will always be some fringe guys in parts of the world who hatch their plots outside of the view of what we're able to observe. The only options you have are to limit their access to harmful weapons/devices, or contain them as fast as possible when they do go on the offensive.

Yes, doctors and other emergency responders did a great job, but don't be so quick to take away a victory from law enforcement when there are very few positive stories circulated about them ever. The boston marathon runners/crowd didn't know they were putting their lives on the line that day. Law enforcement, on the other hand, made a conscious decision to do so.