It’s not clear how many law enforcement agencies have purchased the tool, called Rekognition, since its launch in late 2016 or since its update last fall, when Amazon added capabilities that allow it to identify people in videos and follow their movements almost instantly.

The Washington County Sheriff’s Office in Oregon has used it to quickly compare unidentified suspects in surveillance images to a database of more than 300,000 booking photos from the county jail — a common use of such technology around the country — while the Orlando Police Department in Florida is testing whether it can be used to single out persons-of-interest in public spaces and alert officers to their presence.