The EFF identified dozens of license plate readers with insufficient security (and many with no protection at all). You can read the full article which mentions one of my blog posts with my research on the devices!
Independently, a researcher named Darius Freamon found that you could access the control panels via Telnet and generate statistics about plate captures. Building off Freamon’s work, a team of computer scientists at the University of Arizona dug further into the data and found vulnerable cameras in Washington, California, Texas, Oklahoma, Louisiana, Mississippi, Alabama, Florida, Virginia, Ohio, and Pennsylvania. The largest cluster was in southeastern Louisiana.