The Nazis stole thousands of artworks from Jewish families during World War II and the restitution of these pieces has been a slow process involving legal battles, complex searches and some stunning finds.
Ahead of a court ruling on the return of a painting by impressionist master Camille Pissarro this week, here is some background.
Plunder and rescue
The art plundered by the Nazi regime was intended to be resold, given to senior officials or displayed in the Fuehrermuseum (Leader's Museum) that Adolf Hitler planned for his hometown of Linz but was never built.
Just before the end of the war, the United States dispatched to Europe teams of experts -- museum directors, curators and educators -- to find, protect and rescue cultural treasures.
Known as the Monuments Men, they were honoured in a 2014 George Clooney film of the same name.
These work and restitution programmes enabled the return of most of the looted works to their owners soon after the end of the war.
But out of 650,000 stolen pieces, about 100,000 had not been returned by 2009, according to figures released at the Holocaust Era Assets Conference in the Czech Republic that year.
A sculpture by the French artist Auguste Rodin from the collection of late German collector Cornelius Gurlitt is pictured during the preview of the exhibition on November 1, 2017 at the Bundeskunsthalle in Bonn AFP
Works seized by the Nazis in France were stored at the Jeu de Paume site in Paris, originally tennis courts, ahead of their shipment to Germany.
Thanks to the secret notes of Rose Valland, an art historian there, about 45,000 were recovered and three-quarters of these returned, according to a report to the French Senate in 2013.
Of the remaining "orphaned" pieces, some were sold and more than 2,000 were accorded the special status of "MNR", standing for ”Musees Nationaux Recuperation" (Recuperation - National Museums) meaning they are provisionally entrusted to museums.
The works were exhibited from 1950 to 1954, but then, "for 40 years, nothing happened", said the 2000 Matteoli report on the looting of French Jews.
The report noted "the total abandon of all searches for the owners of these works".
Inertia settled over the restitution drive in the context of the Cold War and the complexities of various cases.
The process was revived in the 1990s after the declassification of thousands of archives and the publication on the internet of databases such as The Art Loss Register.
In December 1998, 44 countries signed the Washington Declaration that committed them to stepping up efforts to return stolen pieces to their prewar owners or heirs.
This led to the creation of special commissions and new laws, including the US Holocaust Expropriated Art Recovery Act of 2016 that lengthened the time limit for lodging a restitution claim.
The Klimt affair
In one of the biggest cases involving art stolen by the Nazis, five masterpieces by Gustav Klimt were caught up in a bitter legal battle between a descendant of the Jewish family from which they were taken and Austria's Belvedere Museum.
They included two stunning portraits of Adele Bloch-Bauer, completed with gold leaf.
The Vienna museum argued that Bloch-Bauer herself had left it the works. But American heiress Maria Altmann disputed the claim, saying the pieces belonged to her uncle, Adele's husband.
Altmann won her battle in 2006 and the pieces were returned. The story was adapted by British filmmaker Simon Curtis into "Woman in Gold" (2015).
Austria estimates it has returned about 10,000 works from public collections after passing a restitution law in 1998.
A visitor looks at a catalog in front of a painting by Claude Monet from the collection of late German collector Cornelius Gurlitt during the preview of the exhibition AFP
A spectacular find
In 2011 a raid on a rubbish-strewn flat in Munich as part of a tax investigation uncovered hundreds of priceless paintings, including works by Picasso and Matisse, that had been stolen by the Nazis.
The flat belonged to Cornelius Gurlitt, an octogenarian whose father was one of four art dealers charged by the Nazis with selling the art.
An additional 239 works were found at a house he owned in Salzburg, Austria.
Gurlitt passed away in 2014 and left his collection to the Museum of Fine Arts in Bern, Switzerland. But many of the pieces have been subject to legal challenges across Germany.