Actually a scan is needed to get the proper size.
QUOTE
The researchers say they were able to open Threat Level's lock with covert methods because they were able to determine the angles of the bitting from the scanned picture of the key. Had the picture been poorer quality, they still could have created a key to lift the pins, but they would have had to use a forced-entry technique to break the cylinder and open the lock.
But many thieves don't just 'use' keys they have in their possession because they would be immediately suspect. Instead they would try to make a duplicate that could be used when the original is not in their care. This gives a false sense of security to some in management who think that key is non-reproducible.