Flock provides police departments with networks of surveillance cameras — primarily, automatic license plate readers that photograph each vehicle that passes them. | NurPhoto via Getty Images To no small extent, Americans have grown accustomed to being watched. For more than a decade, CCTV cameras have recorded a hefty portion of many people’s public movements, while ubiquitous smartphones have made us all perpetually vulnerable to unsolicited documentation (if not, social media notoriety). Until recently, however, technical limitations constrained the reach of government surveillanc...