The innocent should fear facial recognition, too

SIR – Malcolm Greenhill (Letters, July 15) believes that we have nothing to fear from facial recognition.

Why not go the whole hog and implant microchips into babies at birth? The state would then hold endless information about all of us.

We take our freedoms and democracy for granted. A totalitarian state could easily abuse such information.

William Rusbridge

Tregony, Cornwall

SIR – Duncan Ball, Deputy Assistant Commissioner at New Scotland Yard (Letters, July 15), says facial recognition technology was “thoroughly evaluated throughout the trial period” and “on average, there was a false-positive identification rate of one in 1,000”.

This figure is neither reassuring nor very helpful. To judge the validity of a test, you also need to know the false-negative rate. Moreover, it helps to know the incidence of the thing you are testing for.

At a wild guess, one person in 10,000 chosen at random will be “wanted” (subject to a warrant not backed for bail and with a biometric picture on file). If the Met Police point their cameras at the crowds leaving London Victoria station in the morning (where there are around 100,000 two-way passenger trips a day), they will end up detaining or questioning 100 innocent people. They may or may not also catch some or all of the 10 wanted people (depending on the unknown false-negative rate).

They will also build up a database (illegal under current law) of the faces of 99,990 presumed innocents.

Mark Hodson

Bristol