The example of a daring Realist painting by Gustave Courbet that I usually teach in my Humanities course is the famous Enterrement à Ornans (shown at the Salon in Paris in 1850). Because the students in this class are 10th graders, I obviously could not teach this much more daring Courbet painting, L'Origine du Monde (1866), which is not for the faint of heart, so be warned! As I learned in a fascinating article by Véronique Maurus (Courbet le peintre, in Le Monde's print edition of July 29, 2003), Courbet's fame around the world after his succès de scandale in Paris in the 1850s brought him a number of foreign commissions of landscapes, genre scenes, and nudes. The most provocative of these nude paintings was ordered by an Ottoman diplomat, Khalil Bey (1831-1879), who was an avid collector of erotic art. He also owned Ingres's Bain turc (1862, now in the Louvre) and Courbet's Les dormeuses (1866, now in the Musée du Petit Palais).
L'Origine du Monde was kept in private collections, most notably that of French psychoanalyst Jacques Lacan, who displayed it at his country home in Guitrancourt, behind a wooden cover with a sketch done by André Masson in 1955 that suggested the painting beneath it. The painting is now in the collection of the Musée d'Orsay in Paris. Apparently, although new to me, this painting is not a secret: Christine Orban has written a novel called J'étais l'origine du monde (Paris: Albin Michel, 2000), narrated by the woman who was possibly the model for this painting, Joanna Hiffernan (b. 1842/43), the Irish woman who left James Whistler to become Courbet's mistress. She is definitely shown, clothed, in Whistler's Symphony in White, No. 1: The White Girl (painted in Paris in 1861-62, shown here with a study he did; this painting is now in the collection of The National Gallery here in Washington) and Courbet's Jo, la Belle Irlandaise (1866, one of the four versions at the Met) and Les dormeuses (see link above).