They match faces out of a crowd for criminals, but to be a criminal you have to have committed a specific crime... usually that means a single person. For any one crime, they are looking for a single person and that's worst case for false positive recognition. For a large sample set 50k-1000k, they are lucky they don't match any one person to multiple criminals (birthday paradox) ... that would be obviously disqualifying.
I suppose it could be worse and they just take an aggregate face of all (accused?) criminals or for particular crimes (white collar?) and match against that... hey your skin was brown, or hey you didn't shave... you appear Male.
I suppose it could be worse and they just take an aggregate face of all (accused?) criminals or for particular crimes (white collar?) and match against that... hey your skin was brown, or hey you didn't shave... you appear Male.