[Stuart]

IIRC, years ago, on Tommorrows World, they had a cash machine that used signature recognition instead of pins (as well as the image of the signature, it also used the timing and angle of the individual strokes within it, thus making the signature almost impossible to forge).

The way it worked was interesting. It was invented by an RAF engineer, who used Ultrasound to detect fractures in jet engine casings. He came up with the idea of using the same technology in cash machines, and found that when objects were placed on the machine while it was scanning itself, it caused the results of the scan to change.

Maybe this technology could be looked at again.

Still, they seem to have forgotten about the technology