With 25,000 National Guard members set to protect D.C. for Joe Biden's inauguration, each member has been subject to a heavy vetting, which includes high-tech facial recognition.
Federal law enforcement sources tell us ... FBI vetting -- which is normal for high-security events -- begins by checking social media accounts, looking for connections to extremist groups.
Along with reviewing posts, comments and photos ... we're told the feds are using facial recognition software to track the activities of guardsmen and women, specifically searching for photos or videos tying them to radical activities.
Our sources say all 21,000+ National Guard members currently in D.C. -- who have come in from all 50 states -- have been scrutinized by facial recognition and other high-tech methods to determine if they had any involvement -- direct or indirect -- in the Capitol riots.
As for how that works ... all Guard members were required to take a photo when they showed up in D.C. for duty. We're told that photo is then cross-referenced with security camera footage along with online content to make sure there's no connection to extremist, far-right or fringe groups.
Along with the high-tech vetting tricks, our sources say the more common criminal background checks are also conducted ... in order to pick up on any red flags such as arrests or police report mentions.
When it's all said and done ... the FBI's goal is obviously to weed out anyone who might not have national security as their top priority while serving with the National Guard.
A U.S. official announced Tuesday, 2 Guardsmen apparently fit into that category and were removed from the inauguration security detail ... after the vetting process determined they had ties to far-right extremist groups. Later, that number was reported to be "about a dozen."