“Several companies operate independent, non-law enforcement ALPR databases, contracting with drivers to put cameras on private vehicles to collect the information.”
https://www.eff.org/pages/automated-license-plate-readers-al...
Motherboard did a deeper dive on one of them:
“DRN is a private surveillance system crowdsourced by hundreds of repo men who have installed cameras that passively scan, capture, and upload the license plates of every car they drive by to DRN's database. DRN stretches coast to coast and is available to private individuals and companies focused on tracking and locating people or vehicles.”
https://www.vice.com/en/article/ne879z/i-tracked-someone-wit...