From the Daguerreotype to the selfie, photography has changed how we see the world and how we document our lives. As a way of understanding the medium's vast history, Ian Haydn Smith looks at 50 key photographs that document important milestones for the art form. Described in succinct texts and shown in images, here are Steve McCurry's stunning portrait of an Afghan girl, Alexander Rodchenko's wrenching close-up of his mother, and Dennis Stock's iconic 1955 shot of James Dean walking in the rain, plus images by Nadar, Ansel Adams, Julia Margaret Cameron, André Kertesz, Robert Capa, Cindy Sherman, and others.