Your Driver's License and Finger, Please

In Greenbay, Wisconsin, Police have begun fingerprinting people on routine traffic stops:

"If you're ticketed by Green Bay police, you'll get more than a fine. You'll get fingerprinted, too. It's a new way police are cracking down on crime.
If you're caught speeding or playing your music too loud, or other crimes for which you might receive a citation, Green Bay police officers will ask for your drivers license and your finger. You'll be fingerprinted right there on the spot. The fingerprint appears right next to the amount of the fine."

Why don't they just go for the DNA while they're at it? What won't they do to "protect and serve?"

See Update.