Bottom Line is simply that (here in the USA) when one is in a public or open area, the right to explicit privacy is forfeit. This means if person A is in a park or other public venue, person A is within their right to photo/video anyone else in the same public venue. Person B should NOT expect a full right to privacy when in a public area. However, Person A may NOT approach person B's docile and expect to be free to photo person B through their windows. That is definitely invasion of privacy. When in a public area, it becomes very unfortunate that some persons would take advantage to photo nothing but little children. Not acceptable, but legal! ("I'm compiling photos for youth sports and potential injuries.") Yeah right! But, still legal. The bottom line here is that even with a zoom lens, one is wholly permitted to legally photo/video in the open domain/public areas. Courts have ruled individuals should expect their right to privacy to be forfeit if they are in a public area, i.e., city park, city streets/sidewalks, open spaces, public transportation, virtually anywhere that is not of a private venue. The one thing any photographer/videographer must remember is that while it is permitted to photo/video another person in public, there comes a potential point in time when harassment sets in. Respect others privacy, and if they do happen to object, don't take their photo/video or assure them you will blur their face if features are distinguishable.