Short answers, pulled from the story.
Photojournalism is journalism that uses still or video images to tell a news story. It is distinguished from documentary, war, street, and celebrity photography by a strict ethical framework requiring an honest, impartial, and strictly journalistic approach.
The first photograph used to illustrate a newspaper story was a depiction of barricades in Paris during the June Days uprising, taken on the 25th of June 1848 and published as an engraving in L'Illustration on the 1st-the 8th of July 1848.
Magnum Photos was founded in 1947 by Robert Capa, David Seymour, Henri Cartier-Bresson, George Rodger, William Vandivert, Rita Vandivert, and Maria Eisner. It is one of the first photographic cooperatives, owned and administered entirely by its members worldwide.
The Golden Age of Photojournalism is generally considered to span roughly the 1930s through the 1950s. It was enabled by the compact commercial 35mm Leica camera introduced in 1925 and the development of the first flash bulbs between 1927 and 1930, which gave photographers true flexibility in the field.
Photojournalists face ethical decisions about what to photograph, how to frame subjects, whether to publish images of violence or the dead, and whether stage-managing a shot constitutes fabrication. Photo manipulation, false captioning, and questions of subjects' right to privacy are also ongoing concerns, complicated further by the rise of digital editing tools.
Digital cameras, mobile phones, and social media have dramatically changed how news images are gathered and distributed. By 2016, major U.S. newspapers including The New York Times, The Wall Street Journal, and The Washington Post relied on freelancers for the majority of their visual coverage, and staff photojournalism positions shrank significantly through the 2010s.