"Studies by the Imperial navy and others have already discovered that the cloud separated, but the photo confirms it and is thus valuable," a museum official told the Japan Times.
The photo had appeared in history books about Hiroshima, but the whereabouts of any copy of the photo or the negative was unknown until now, according to the museum. (...) The materials were contributed by a late survivor, Yosaburo Yamasaki, in or after 1953. It is not known who took the photo. It will be displayed at a museum located next to the school from this spring.
Along with Japan Times, AFP reports that the black-and-white photo was likely taken some 30 minutes after the bombing on August 6, 1945, roughly 10km (6 mi) east of the impact center. That site is located in what is now the town of Kaita, Hiroshima Prefecture (Google Maps link).
"The existence of this shot was always known in history books, but this is the first time that the actual print has been discovered," a curator at the Hiroshima Peace Memorial Museum told AFP. "A shot showing the mushroom cloud split into two like this is very rare." More at Discovery News.
(Image: HONKAWA ELEMENTARY SCHOOL / AFP)