Roscher was born in Nuremberg and trained as an artist throughout Europe. He attended the Royal Academy, Munich; the Accademia di Belle Arti, Florence; and the Sorbonne, Paris. He was active as a portrait painter from the 1910s until his death in 1968, first in Europe, and eventually migrating to the Americas. He had homes in both Missouri and Pennsylvania, and also worked in Palm Beach County, Florida where he maintained a studio in the south wing of the Breakers Hotel for more than a decade.
Roscher painted royalty, socialites, and eminent religious, political, and judicial figures. His sitters included Pope Benedict XV, who knighted him Cavaliere di San Gregorio Magna; Pope Pius XI; Supreme Court Chief Justice Frederick Vinson; King Ludwig and Queen Therese of Bavaria; and Eleanor Roosevelt among others. He also painted a number of provocative nudes.