Legal Question in Technology Law in California

As to the first question, whether you can publish pictures of people is not going to be determined by whether they were on public land, nor by whether you were on public land, at the time the pictures were taken.

It is not illegal to publish pictures of people, regardless of the location of the photo, as a general principle. It is a form of free speech.

However, there are some important exceptions to the principle. One of these is that if you unduly invade someone's privacy, you may be sued by that person for damages. If no damages have been suffered, however, the lawsuit will turn out to be a waste of the plaintiff's time and money (and yours too), because the plaintiff won't recover any damages.

Another exception is that you cannot capitalize on someone's image for profit, whether or not the person is a celebrity, without their permission. This principle may require producers of films for commercial use, advertising agencies selling pictures for ad purposes, etc., to get prior permission from their "subjects."

I do not know of any principle giving anyone a right to sue you for photographing herds of grazing cows for profit. Out here in dairy country where I live, artists are painting local cows all the time, and they sure plan to sell those paintings.