The 74 photographs in the show at the Simon Tracy Gallery in Marylebone, north-west London, were taken by the American ethnologist Edward Curtis between 1900 and 1928.
Curtis carried out the largest photographic record made of American Indian life. He took 40,000 pictures, of which 2,300 were attached to a 291-edition, 20-volume work he produced on his researches.
His work was supported by President Roosevelt, who wrote in a foreword: 'Our generation offers the last chance to do what Mr Curtis has done. He has caught glimpses into that strange spiritual life and mental life from whose innermost recesses white men are forever barred.'
Curtis recorded the costumes, rituals and lifestyles of 80 American tribes in more than a score of US states and Canadian provinces.
Despite Roosevelt's generally accurate claim that non-Indians were 'forever barred' from the 'innermost recesses' of Indian spiritual life, Curtis did become deeply involved in his subject, both professionally and spiritually. He was the only white man to be enrolled as a Hopi Indian priest - and took part in the ultra-secret 16-day Hopi Snake Dance, perhaps the most famous of all North American Indian rituals.
While photographing (and making sound recordings) of Indian life, he tried to live as the Indians did - and once almost lost his life while trying to catch giant octopuses with his hands. The Indians called him 'Shadow Catcher'.
Before the First World War there was great public enthusiasm for his work. But from 1914 until the Seventies, interest was low. Recent years, however, have seen a resurgence: a set of his 20-volume work (complete with its 2,300 pictures) sold at auction last year for dollars 360,000 ( pounds 243,000).
Curtis died, aged 84, in 1952.
He spent many years in a Denver hospital suffering from physical and mental exhaustion and ended his days in anonymity on a Californian farm raising ducks and chickens.