I don't know why. Good observation. I guess the whole lobby card picture is a reverse image. Three possible clues: (1) the movie was made in 1941; the lobby card is from the circa 1949 re-release; (2) the actual film is in black and white; and (3) the film was not made by a major studio -- made by Arnold Pressburger Films [us] (as Arnold Productions Inc.). Released by a no-name outfit: Film Rights, Inc.. so maybe cheaply made lobby cards?

Robert