Dr. Stadelmann (1922) by German Expressionist painter Otto Dix.
The Scream (1893), by the Norwegian painter Edvard Munch, an important precursor of German Expressionism.

Hitchcock's Strangers on a Train: the portrait of St. Francis by Bruno Anthony's unbalanced mother. Bruno takes this as an image of his father, thus bringing in Freudian psychology as well.

Expressionism was an art movement associated mainly with German painting and film of the early 20th century, particularly following World War I. Expressionism had a strong influence on American film noir, due to the migration of German directors to Hollywood in the 1930s. Hitchcock was very much aware of Expressionism, from his interest in modern art and from having worked in German film industry in the 1920s.

The goal of Expressionism was to evoke the subjective responses that the artist has to objects or events. It contrasted with impressionism, which sought to capture the outward impression of an object or scene. Expressionism did not attempt a realistic portrayal of the world, but rather the extreme and distorting emotions that the world causes in the sensitive individual.

The stylistic premise of Expressionism was that the artist's response to the environment was so intense that it affected the form of the art. Surface elements are distorted or exaggerated by subjective pressures. As a reflection of the times, Expressionist painting tended to be vivid and violent, with jarring images.

George Grosz, Metropolis: Grossstadt (1917), left, and Street Scene (1925). In German Expressionism, settings are typically urban, crowded, often chaotic. Perspective is distorted and colors are dictated by feeling more than realism. Grosz is an acknowledged source for the visual design of Fritz Lang's movie M (1931).
Christian Schad, Count St. Genois d'Anneaucourt (1927), left, and Otto Dix, To Beauty (1922). Claustrophobic urban settings convey a strong sense of unease; situations are fraught with sexual tension, often overtly or implicitly violent.

Three portraits by Otto Dix: Sylvia von Harden (1926), Anita Berber (1925), and Lady with Mink and Veil (1920. In Expressionism, female figures are a particularly strong source of the uncanny.