From a newspaper report dated 13 December 2013: Police broke into the flat of Cornelius Gurlitt, the son of a Nazi art dealer who hoarded hundreds of works believed to have been looted by the Third Reich. Gurlitt has been the focus of huge media attention after a trove of over 1,400 previously unknown masterpieces were uncovered in his Munich flat. A task force appointed to research the origin of the art has said that around 590 pictures fall into the category of art looted or extorted by the Nazis from Jewish collectors. These include pieces by Picasso, Matisse, Munch and Cezanne among others.
Originally slated for a December 2013 release, with an awards/holiday season aim. In a rare move, Director George Clooney asked the studio for more time for post-production due to the special effects not being ready, knowing this would make it very unlikely to receive awards attention (uncommon for an early-year release). Reluctantly, the studio put it to the following February.
When Sam Epstein (Dimitri Leonidas) sees a Rembrandt's painting for the first time (a self-portrait from c.1645), his face is lit with a Rembrandt style (a key light coming from a side of the frame creates a chiaroscuro marking a small triangle on the cheek not receiving the light directly.)
As mentioned in the jail scene between Matt Damon and Cate Blanchett, the office in Paris where the Nazis amass their stolen art was the Galerie du Jeu de Paume, located next to Place de la Concorde in the heart of the city. The real Hermann Göring visited the museum 20 times during the war and cherry-picked over 700 items for his private collection.
The character of Claire Simone, played by Cate Blanchett appears to have been based on Rose Valland, a Parisian museum curator who was drafted by the Nazis during the occupation of Paris to assist with art acquisitions. As depicted in this film and in the documentary The Rape of Europa (2006), Valland secretly kept a detailed ledger of all works that passed through Nazi hands, the original (often Jewish) owner of each work, and the location in Germany where each item was eventually transported.