In Texas, the government has put a magnetic stripe on the back of a driver's license and State ID cards. The stripe can be scanned to verify the information on the front. Bars and clubs have scanners to check id's for the true age of the id holder. The idea of the magnetic stripe was that a police officer could scan the license and be told that you are a white male, brown hair, green eyes, 180 pounds, 5 feet ten inches tall. If someone has altered the photo on the front of the license the scanner will tell the police what the original owner of the id looks like.
However, the magnetic tape could be used to store other information. Your blood type. Medicine that you are allergic to. Whether you are an organ donor. OR, whether you are considered a "bad driver", whether you have ever been arrested for drug possession, whether you are a member of the Democratic party or in some other way are "An Enemy of the State".
I had stopped carrying a drivers license when I was out taking a walk or riding my bike. A police officer appeared to have a stroke when I told him I do not carry an ID. He felt compelled to bounce me off his police car a few times to find out whether I was concealing an ID. So, now I find it "healthier" to carry an ID when I ride my bike.