This scheme will work for one branch in Lesser Nowhere, Sechwan Province, with a finite and small set of pictures, and a small number of crooks. Once the number of faces increases, the probability of a false positive explodes, roughly as (N 2) (select every two out of N), where N is the size of the pools of pictures + the person being scanned.
The well-known example is the "birthday paradox", in which twenty-three people at a party increases the probability of two of them having the same birthday to fifty-fifty. That particular case was because the actual probability was multiplied by (25 2) = 25! / ((25-2)! * 2!) = 6900 comparisons being made, times 1/365 chances of a hit.
The German federal security service considered using one of my then employer's recognizers for airports to catch terrorists, but ended up facing the problem of accusing grandma of being part of the Bader-Meinhoff gang (;-)) No matter how accurate we were, a few more people in the pool would give us false positives. We'd need roughly an accuracy of 99.9 followed by roughly as many decimal places of 9s as there were powers of ten of people.