I think this is just a scare tactic by the highway patrol because simply recording a license plate like this isn't going to prove their case. I doubt that any state has a law that says one of their residents can't own a vehicle that is registered in another state. But every state will have a law about how long that vehicle can be in the state without the plates being changed. For example I live in California and if I wanted to keep my motorhome in Florida all the time and just fly out there to use it, it's going to have to have Florida plates on it. And I can even drive it back to California if I want, but I can only keep it in California a very limited amount of time. So just because I may be spotted in California with it, doesn't prove I'm breaking the law.
However, here in California the CHP does have officers assigned to enforce these kinds of things. What they will do is find out where vehicles are and then check on them on a regular basis to see if they ever leave the state. After they determine they have been in the state too long then they start the prosecution process.
