In the UK I have seen on occasions, immigration officials situated after security and stopping people on request, so it is not unheard of if they are looking for anything in particular.
I have also seen in MAN and LHR that if you fly domestic, then a picture is taken of your face when you first scan your boarding pass prior to security and whilst you approach the gate, a second picture is taken when you next scan your boarding pass and a cross check to verify that the first and second image match.