Courts are currently wrestling with this.

https://www.oyez.org/cases/2017/16-402

> The government's warrantless acquisition of Carpenter's cell-site records violated his Fourth Amendment right against unreasonable searches and seizures. Chief Justice John Roberts authored the opinion for the 5-4 majority. The majority first acknowledged that the Fourth Amendment protects not only property interests, but also reasonable expectations of privacy. Expectations of privacy in this age of digital data do not fit neatly into existing precedents, but tracking person's movements and location through extensive cell-site records is far more intrusive than the precedents might have anticipated.

Or in United States v. Jones (cited in https://www.ca4.uscourts.gov/opinions/201495A.P.pdf):

> Although the case was ultimately decided on trespass principles, five Justices agreed that “longer term GPS monitoring . . . impinges on expectations of privacy.” See id. at 430 (Alito, J., concurring); id. at 415 (Sotomayor, J., concurring). Based on “[t]raditional surveillance” capacity “[i]n the precomputer age,” the Justices reasoned that “society’s expectation” was that police would not “secretly monitor and catalogue every single movement of an individual’s car for a very long period.”

It seems clear these cameras can hit some kind of threshold where they're common enough and interlinked enough to amount to unconstitutional surveilance. We don't know exactly where that threshold is yet.

The courts made polygraphs submittable legal evidence used to convict people, and still use them on people under supervision (because lesser standards apply).

Precedent is often crap and wrong until someone can find a good case paired with good lawyers to rectify.

Edit: Throttled so editing to reply

Precedent is randomly set by whoever gets there first often with a random case and a defendant with zero funds desperate to minimize their situation (for example without the funds to challenge the legality of polygraph/flock versus polygraph/flocks paid 'experts'). Although now political people are trying to game the system and shop very thought out cases to specific friendly courts to help put their finger on establishing precedent. After building enough such cases in lower courts, moneyed interests then shop it to the next level. Then with enough at the next level, to the Supremes.

It's a pretty awful, unintentional by design and fairly random 'legal system' with a huge bias towards those with more money and or the huge disparity in power of the Federal government, it's prosecutors, trial tax and the ridiculousness of 'if you exercise your constitutional rights you risk an additional 20-50 years in prison' versus someone broke, whose life has already been ruined by time in jail (and their fight beaten out of them), just wanting to go home as soon as possible.

And when those disempowered have the courage to risk the trial tax and do happen to stumble upon a win you get the strategic use of either pleas bargains or dropping the case by prosecutors to prevent precedent, or the abuse by judges of 'as applied' rulings in order to again prevent precedent from being set even when the case was won.

One side has all the power. One side has huge threats (in the form of trial tax). One side literally holds in you prison and has 100% control over every aspect of your life as you try to fight them and uses things like diesel therapy or the many other ways the have to apply to break you down for 'being difficult'. One side has the power to just drop cases it if risks precedent they don't like. And one side has the power to label a case 'as applied' to prevent precedent they don't like. It's a pretty crap system if you want fair unmanipulated precedents to come out of it. It's a great system if you want money/federal prosecutors/judges to be able to put their finger on the scale and set the outcome.

The courts have been wrong about many things, sometimes for centuries before they've fixed it. Some things they think they've interpreted correctly now that they'll turn around and interpret some other way later.

Trying to interpret viewing and recording the plate as speech but not displaying it as speech is trying to have your cake and eat it too. If the camera can stalk my car everywhere and record it under auspices of 'speech', it's only logical I can hide it as 'speech.'