Hey! Get the chip off your shoulder. There are quite a few people that do not want their faces in random pictures by strangers
Tough.
You don't have an expectation of privacy when you're out in public.
Aloha
An employee on employer property one is not "in public" And George was spot on.
George may be correct that some people do not want to be photographed. However, that does not make it illegal or improper for a photographer to take pictures in public.
However, an employee on employer property
can be "public". It depends very much on the setting.
For example, let's say I'm standing on a public sidewalk adjacent to a public street, entirely within the public right-of-way. I take a picture of a construction site, and in that picture I capture a worker. Whether that worker is the subject of the picture or is merely incidental to the photograph does not matter for legal purposes. He or she may not want to have been pictured, but that does not matter because he or she is visible from public space
and does not have
a reasonable expectation of privacy.
In the United States, "speech" in public spaces cannot be infringed by the government, except in certain circumstances. Photography is considered a form of speech, and it is almost always legal to take pictures from public spaces. Exceptions include military bases and places where national security is an issue. The courts have ruled that photography of people in public spaces is legal when they do
not have
a reasonable expectation of privacy.
A reasonable expectation of privacy, for example, would be in a stall in a public restroom, or in a bedroom or hotel room visible from the street. If you walk out into a public square or transit platform, you do not have a reasonable expectation of privacy, and you have no power to stop someone from taking pictures.
In
publicly accessible private spaces, like a shopping mall, the owner or an agent of the owner (security guard), can ask you to stop taking pictures. If you do not stop, you can be asked to leave and if you refuse, you can be arrested for trespassing (not for photography).
In
private spaces, you do not have a right to take pictures, but you can certainly do so if you have the permission of the owner.
As far as transit systems and train stations go, those are generally considered public spaces. Sometimes they can be publicly accessible private spaces. At any rate, no one in a public space or a publicly accessible private space has a
reasonable expectation of privacy, and photographers can take their pictures.
You may not like that, but that does not matter.