“This really is the holy grail of Capa work,” said Brian Wallis, the center’s chief curator, who added that besides the Capa negatives, the cracked, dust-covered boxes had also been found to contain Spanish Civil War images by Gerda Taro, Robert Capa’s partner professionally and at one time personally, and by David Seymour, known as Chim, who went on to found the influential Magnum photo agency with Capa.

The discovery has sent shock waves through the photography world, not least because it is hoped that the negatives could settle once and for all a question that has dogged Capa’s legacy: whether what may be his most famous picture  and one of the most famous war photographs of all time  was staged. Known as “The Falling Soldier,” it shows a Spanish Republican militiaman reeling backward at what appears to be the instant a bullet strikes his chest or head on a hillside near Córdoba in 1936. When the picture was first published in the French magazine Vu, it created a sensation and helped crystallize support for the Republican cause.

Though the Capa biographer Richard Whelan made a persuasive case that the photograph was not faked, doubts have persisted. In part this is because Capa and Taro made no pretense of journalistic detachment during the war  they were Communist partisans of the loyalist cause  and were known to photograph staged maneuvers, a common practice at the time. A negative of the shot has never been found (it has long been reproduced from a vintage print), and the discovery of one, especially in the original sequence showing all the images taken before and after the shot, could end the debate.

But the discovery is being hailed as a huge event for more than forensic reasons. This is the formative work of a photographer who, in a century defined by warfare, played a pivotal role in defining how war was seen, bringing its horrors nearer than ever  “If your pictures aren’t good enough, you’re not close enough” was his mantra  yet in the process rendering it more cinematic and unreal. (Capa, not surprisingly, later served a stint in Hollywood, befriending directors like Howard Hawks and romancing Ingrid Bergman.)

Capa practically invented the image of the globe-trotting war photographer, with a cigarette appended to the corner of his mouth and cameras slung over his fatigues. His fearlessness awed even his soldier subjects, and between battles he hung out with Hemingway and Steinbeck and usually drank too much, seeming to pull everything off with panache. William Saroyan wrote that he thought of Capa as “a poker player whose sideline was picture-taking.”