Omni Brain: Blinking in photos

How many photos would you have to take of a group of people to be assured that no one is blinking? This guy figured it out:

...the probability of one person spoiling a photo by blinking equals their expected number of blinks (x), multiplied by the time during which the photo could be spoilt (t) - if the expected time between blinks is longer than the time in which a photo can be spoilt, which it is.

This makes the probability of one person not blinking 1 - xt. For two people it's (1 - xt)(1 - xt) and for a group of people it's (1 - xt)^n, n being the number of people.
This means (1 - xt)^n is also the probability of a good photo. Therefore, the number of photos should be 1/(1 - xt)^n.

Let's test this: each shutter opening results in either a good photo or a spoilt one. If you make a graph of a lot of these successes and you'll find it follows what statisticians call the normal distribution. Even if you know nothing about stats, you've probably heard of the bell curve - well, that's what the normal distribution looks like.

At one end of the curve the trials are 100% successful: the photographer got all good shots. In the middle, the number of good and bad photos is split 50:50. And, at the other end, are all dud trials: the photographer got no good shots.

Piers then figured out how many shots I'd need to be 99% certain of getting a good one. He found that photographing thirty people in bad light would need about thirty shots. Once there's around fifty people, even in good light, you can kiss your hopes of an unspoilt photo goodbye.