A lot of people are upset about Flock cameras. I must confess, I don't like them, but I can't see any way to stop them from what they are doing. It is perfectly legal.
Consider, police can conduct warrantless tails of individuals for days at a time, as long as those tails remain in public areas, public thoroughfares and do not infringe on curtilage, that is, the home and the area immediately surrounding it.
Flock cameras that are not trained on curtilage are viewing public thoroughfares. It is not a crime to publicly observe individuals who are traversing public areas. That's simple observation, and there is no law against it, nor can there be. If it were a crime, cops could not do warrantless tails, but they can do warrantless tails.
Heck, game wardens can walk onto private property, install secret cameras and use the evidence derived in court without bothering to get a warrant. It is not considered trespass and the surveillance is completely legal. As long as the cameras are of woods and open fields, not curtilage, there is zero problem. This has been upheld countless times. Flock cameras are just public highway versions of this "Open Fields" doctrine. The Open Fields doctrine is relatively new, having been established during Prohibition, but it has never been overturned. In fact, SCOTUS was the court that created it (Hester v. United States, 1924). It has been reaffirmed, by SCOTUS, as recently as 1984 (Oliver v. United States). Unfortunately, that's great precedent for Flock.
As I said, I don't like Flock cameras and I have no problem with people who knock them down (which is logically inconsistent of me, I grant), but Flock isn't violating the law.