The Man Ray Rayogram - a camera-less photograph taken by placing objects on light-sensitive paper and exposing them to light from above - is inscribed by the photographer on the back and marked"original".
The find has excited Sotheby's, in London, where the photograph and 248 others, including prints by the American landscape photographer Edward Weston, will go to auction on 2 May. The Man Ray alone is expected to fetch upwards of pounds 30,000.
The auctioneers' photographic expert, Philippe Garner, a senior director at Sotheby's, said yesterday that the discovery of the collection was "possibly the most exciting group of photographs to have turned up in this way in the last 30 years".
Man Ray lived in Paris for much of his working life. He was linked to the Dada and Surrealist movements although he was also known as an experimenter and to a large extent, reinvented photography. He died in 1976.
Mr Garner said the collection was put together by Helene Anderson, a German photographer who gathered most of the photographs in the 1920s and 1930s before the sweep of Nazism stemmed much of the free flow of art in Germany.
In 1939 Anderson boxed up her collection and sent it eastwards, out of harm's way, to her parents in Silesia. Later, as the Russians advanced, the boxes were moved again, this time to Frankfurt where Anderson settled until her death in 1971.
"Helene Anderson had an exceptional eye and understanding for the dynamic developments ... in photography in Germany and elsewhere during the 20s and 30s and set about building a collection to illustrate the finest achievements of the avant-garde," said Mr Garner.
"When she died, her son knew he was left with a number of boxes but did not know what was inside them. Only recently, 25 years after his mother's death, did he realise he might have something important."
The whole collection is expected to fetch something in the region of pounds 650,000.Reuse content