Dennis Stock seemed born with a capacity to spot the shot that would summarize a situation, and epitomize a person. His childlike receptivity, combined with a refined technical skill and delight in risk-taking, informs the unique composition of his images. Ever prolific – since the 50s Stock has generated a book or an exhibition almost annually – there are nonetheless several images that have become icons of their kind. Most are portraits, of either known or unknown subjects. All are taken …