One day in 1908 Pablo Picasso was scrounging through a pile of canvases in the Parisian junk shop Père Soulier, when he spotted a halting portrait of a woman. The shopkeeper offered a bargain: “Five francs. You can paint on the back.” Upon closer inspection Picasso realized the abandoned painting was an 1895 work by Henri Rousseau, known as Le Douanier (“the customs officer”).
