It is unreasonable to expect to not be observed in a public place, but it is reasonable to expect to not be recorded artificially without your knowledge. This goes for all locations, including public ones.
No, it's not. You've probably been photographed or filmed at least once on your way to work today by an innocent tourist or citizen who was shooting something. A building, or a friend perhaps. It seems unreasonable to expect you won't be featured on such photos.
Yes, it is. I can observe innocent tourists and citizens taking photos and avoid them if I want to. The key part you missed was "without my knowledge." I'm not going to obsess over being in the background of the occasional tourist photo, but if I want to avoid it, I can by simply observing the obvious camera and avoiding it. I could even discuss it with them if I really cared for some reason, and possibly have them delete a photo of me.
I am aware of tourist photos and photos by friends. It is reasonable to expect that I'll be in occasional photographs where I am not the subject. I know that. It is reasonable to expect that I won't be the subject of photos without my knowledge or included in detailed photographic records just because I went to a public place. Detailed imagery of your whereabouts and activities should never be expected and should only be legal with a warrant.