Otto Rau was the son of a Dresden lithographer and was trained by Karl Klič, the inventor of heliogravure, between 1880 and 1884. From 1885 he worked as a heliographer in the Reichsdruckerei in Berlin, where he was involved in the development of the heliotype. In 1887 he moved to the art institute of Heinrich Riffarth (1860-1908). In 1891 he became a partner in the company. In 1887 and 1890 he joined the two leading photographic associations, the Freien photographischen Vereinigung in Berlin and the Verein zur Förderung der Photographie, of which he became chairman in 1891. In both associations he gave lectures on printing techniques and presented his own work. His portfolio "Aus dem Berliner Tiergarten", published in 1891, received particular attention. With its twenty plates, he captured the seasonal moods and important sights in Berlin’s largest park. The trade journals were full of praise, especially for the photogravure technique, which was well suited for landscape photographs due to its extended tonal range.
In 1901 Rau moved to Munich and turned to painting. In 1912 he took part in the Munich annual exhibition for the first time. The following year he received a gold medal at the 11th International Art Exhibition for his oil painting Thawing Stream. His artistic talent combined with a special technical talent made him an art photographer who mastered photogravure, as the most appropriate reproduction technique for art photography, with virtuosity. 
City Museum of Berlin INVENTARNUMMER SM 2012-0667
 City Museum of Berlin "Aus dem Berliner Tiergarten. Zwanzig photographische Studienblätter von Otto Rau" https://sammlung-online.stadtmuseum.de/Details/Index/355681 cited Jan 22, 2023