A new online database recording more than 20,000 works of art looted by the Nazis from Jews in France and Belgium during World War Two shows that at least half have yet to be returned to their original owners.
The database, a joint project between the U.S.-based Claims Conference and the United States Holocaust Memorial Museum, is based on records the Nazis produced in Paris, and is designed to help families search for art they believe may have been seized.
"This is probably the most famous of the (Nazi) looting, and was done in Paris," said Wesley Fisher, director of research at the Claims Conference.
"The general assumption is that most of these things have been returned, but it turns out not to be true," he told Reuters.
The organization, which seeks to return art stolen by the Nazis to its original owners, advised museums, art dealers, auction houses and affected families to consult the listing.
The database includes unrestituted works by artists including Claude Monet and Paul Cezanne, whose paintings can fetch millions of dollars at auction.
The Claims Conference, or Conference on Jewish Material Claims Against Germany, said the 20,000 objects on record were taken from more than 200 private Jewish collections in German-occupied France and Belgium between 1940 and 1944.
A special Nazi task force gathered hundreds of thousands of art objects and millions of books and archives stolen from Jews and others, as well as from museums and libraries.
In Paris, the task force documented each of more than 20,000 objects on index cards or inventory lists.
The Claims Conference estimates the total number of Nazi-looted artworks at 650,000, of which 100-200,000 are still missing. It aims to follow up its new free online resource with a similar initiative in Ukraine.
The issue of restitution of Nazi-looted art is still a sensitive one, not least because of the high value of some of the works in question.
In 2006, Ronald S. Lauder paid a reported $135 million for a Klimt portrait of Adele Bloch-Bauer, whose niece was awarded the work and four others following a restitution battle with the Austrian government.
The deal was brokered by Christie's, which went on to auction the remaining four works for a combined $192.7 million.
In 2008, Sotheby's sold restituted or settled works worth $90 million, including a $60 million Kazimir Malevich returned to the artist's heirs after a museum in Amsterdam was forced to hand it over.
The database can be found at www.claimscon.org/