The Art Loss Register’s Sarah Jackson on recovering art stolen by the Nazis: “In the past, provenance was important to establish value. Today, provenance is taking center stage because of liability. The law is changing slowly, but remorselessly, in favor of the victim. Once there is a known Holocaust survivor of a known work of art, it becomes virtually unsalable. For commercial art dealers, the choice is stark, because the buyers will choose an alternative that is not a tainted work of art.”