[Manuel_D]

Why would it fall apart? The plain view doctrine holds that the police don't need a warrant to observe things in plain view. Like your car driving on the public roads.

Privacy laws are generally about protecting what you do in private, not in public. In the US, anyone can film you in public, government or otherwise.

[filup]

It hasn't been articulated in court. But what flock has essentially done is created a GPS system without satilites.

See Jones vs USA.

Sufficiently saturated ALPRs across the country give you the same capability of GPS. Without GPS.

[Manuel_D]

Jones vs USA involved physically interacting with a person's vehicle. Furthermore, the device would track users even if they were on private property.

By comparison Flock only operates in public, in places that are in plain view.