The old-style F1250s could lend themselves to a bit of fun....
When I was at Wattisham, one evening we found that 'Wee Stevie' had gone flying and had left his F1250 in his SD cap. So, a few minutes with a black chinagraph added a different hairstyle, horns and spectacles etc.... Come the next day, as Wee Stevie showed his pass at the barrier, the guard pi**ed himself with laughter. WS nearly had a sense of humour failure until the guard showed him the F1250 - he hadn't spotted our art work until then. But he did see the funny side of it, being the good chap he was.
The other story I heard of fake ID photos was of a chap employed at AWRE who went around with a photo of Kruschev in his pass for weeks until someone noticed. Then he was fired!