It appears, memorably, in a snapshot taken in May 1945 of American soldiers on the steps of Neuschwanstein Castle in Bavaria — a painted portrait of a woman in a shimmering gown with porcelain skin and curly silver hair.

The portrait and two other old master paintings are held by American soldiers in combat fatigues who have just liberated them from a Nazi storehouse of looted art.

The G.I.s were helping the Monuments Men, a special U.S. Army unit that tracked down millions of works of art stolen by the Germans during World War II.

The image became a resonant depiction of the unit’s role in undoing Nazi evil and restoring part of European heritage to its rightful place.

Now the portrait, by the French court painter Nicolas de Largillièrre from the era of Louis XIV, is to be auctioned next month at Christie’s.

Marc Porter, chairman of Christie’s Americas, said he expected the connection to the historic photograph to attract potential buyers. “The Monuments Men photographs taught the world about the Nazi spoliation,” he said. “This is not the story of a restitution of a work that’s enormously valuable, but it has the depth of the story and the history.”