Since the discovery of a long-hidden trove of masterworks in Germany last year, advocates have sought to shine a spotlight on looted artworks hiding in plain sight.

In other words, those hanging on the walls of Europe’s great museums.

Enter France, known as the art attic of Europe before World War II and where tens of thousands of works were taken from Jewish families by the occupying Nazis. Today, more than 2,000 pieces returned to France after the war — including canvases by Claude Monet, Peter Paul Rubens and Max Ernst — remain in the custody of the Louvre, the Musée d’Orsay and other celebrated French institutions.