Oh, long after the system I worked on was replaced. Back in 1997-1999 the images were filenames in a database record, and we just read the image file and printed it on the card. Then at a later stage a camera looked at the printed card and compared it to what it should look like. We also used to 'etch' the same photograph into the 'laser' (CD-like) golden strip on the back of the card. When you wrote data to the laser strip, it changed the appearance by darkening it. There was an API library supplied by the manufacturer of the encoder drives that could write a visible image to the strip. Not sure if the modern cards still have that feature.