ICAO (International Civil Aviation Organization), an agency of the United Nations, adopted standards for the use of facial recognition technology are the standard for the digital facial image/photo required by the Real ID Act. Facial recognition maps your face, converts your biometric sample, the photo, to numbers which results in your facial image mathematically being stored in a database. The standard called for is hidden in the NPRM (Notice of Proposed Rulemaking) issued by the DHS.
http://www.stoprealidcoalition.com/index2.php?option=com_wrapper&view=wrapper&Itemid=12 page 68 footnote 17, at the bottom of page 68. Nearly no state or national lawmakers understood the significance of the aforementioned footnote. Even today many groups that are opposed to Real ID call Real ID a national ID card. It is much more given the standards for Real ID and the organizations that played a role in U.S. policy, law and the implementing of the law, Real ID Act 2005. Real ID is international ID. It's sister, the EDL (Enhanced Driver's License) is used in lieu of passports.