[Cryptography] Recognizing faces vs. recognizing a face

[Christian Huitema]

> 
> On Mar 1, 2020, at 8:25 AM, John Levine <johnl at iecc.com> wrote:
> 
> This question seems vaguely cryptography related, I hope.
> 
> It seems to me there are two rather different applications called
> facial recognition.
> 
> One is comparing an image of a person to a stored picture and deciding
> whether it is the same person, yes or no.  That's used in various
> countries' automated immigration kiosks, and I think Heathrow airport
> uses it to check that the person who gets on the plane is the same
> one whose passport they checked at security.
> 
> The other has stored pictures of people of interest, and a stream of
> images of people typically from live video, and compares all the
> people in the pictures to all the people in the images, looking for
> matches.
> 
> The accuracy numbers I've seen all seem to combine the two.  Are there
> separate analyses?  I would imagine that the single match would be a
> lot more accurate than many to many.

The two questions that you describe are the same problem. Take the "same person in photo" question. You have to measure false negatives, i.e., present N other pictures of the same person and see how many are not recognize. And you have also measure false positives, i.e., take N pictures of other people and see how many are falsely recognized. You need the two numbers to characterize a system.

-- Christian Huitema