How would cctv know what someone 'at risk' looks like? Facial recognition isn't magic you know. And why would we need some dystopian style technology to monitor

How would cctv know what someone 'at risk' looks like? Facial recognition isn't magic you know. And why would we need some dystopian style technology to monitor your every move to know you're sick, when you can just tell people? Those aren't very good examples.