Are photos staged? sometimes, yes. But also, sometimes, no. They just represent opportunistic events in front of the shutter.

I assure you, the "mounted police charging striking miners" picture was not posed.

I think "renaissance drunk man in the street" is not posed. Nor, "lovers kissing in the riot"

On the other hand "Italian men go ooga-wooga-booga as pretty girl walks by" was totally set up.

"pretty hippy girl puts flower in riot police gun" was probably a repeat, of something started spontaneously.

"dancing man" at the end of WW2.. unclear. "kissing couple at the end of WW2".. unclear. "2 seconds before the ramp opens on D Day" not posed. "Lee Miller in hitlers tub" -posed

"lee harvey oswald shot by jack ruby" is probably not staged. Ask the Warren Commission.

This is a complicated topic. These days you can shoot in bursts, I don't remember the top rates you can achieve with high-end mirrorless/DSLRs, but it is a wild number. While some take this for granted, it's still a relatively novel technology. On the other hand, famous photographers in the past did not have such luxury. I love film cameras, but taking a truly good picture with one that was manufactured up to the early 70's requires years and decades of experience, and luck, especially when the subject is moving.

Probably the most famous example of an ongoing debate regarding authenticity is Robert Capa's Falling Soldier [1].

[1]: https://en.wikipedia.org/wiki/The_Falling_Soldier