It does occasionally happen, sometimes the photo gets detached or is too out of focus for either the biometric or manual identification to work. If the passenger does not have an EU passport on them then a Border Force officer may need to be summoned, at which point the passenger may well be offloaded. Not a good situation, but it happens on much less than 1 percent of flights.
The first thing they try is to get someone from HAL security over to recover the photo, they are usually quite quick to arrive, but a TRM may try to cut losses and offload people quickly. Doesn't always work!
Last edited by corporate-wage-slave; Jun 7, 2016 at 4:07 am