The fingerprint information stored on TWIC and PIV cards is simply a set of minutiae (see http://en.wikipedia.org/wiki/Minutiae for more details) which is also referred to as a template.

When verifying identity, a fingerprint sensor converts the cardholder's scanned image to a second template which is compared with the template stored on the person's card.

If a match occurs then it is known that the card belongs to the cardholder. Meanwhile, the scanned image itself is never saved.

That's not to say that it couldn't… which opens the door for skimming the scanned image. I would be more concerned about that aspect.