Currently the "Real ID Act 2005" is federal law. The Real ID Act calls for federal guidelines for state driver's licenses. The standard for the digital facial image/photograph is an international standard adopted by the International Civil Aviation Organization, an agency of the United Nations.
The standard is specifically called for in order that the digital facial image/photo is facial recognition compatible. Facial recognition is a biometric. Biometric is defined as "measurement of the body". Most often we think of fingerprinting when we think of a biometric. DNA is a biometric as well. Facial recognition is based on measuring the distances between key characteristics of a person's face (center of eyes, nose, ears, lips and so forth). This process is called "mapping" the face.
In 2001 facial recognition technology was used to capture the image of the people that attended the "Super Bowl". The captured images were then compared to law enforcement databases. Since 2001 facial recognition has been used many times in public places. A person's facial image is captured either by the use of CCTV (Surveillance cameras or hand held biometric devices, similar to cameras that connect wirelessly to databases).