WASHINGTON, May 16 (Reuters) - The White House said on Monday that a Newsweek report based on an anonymous source had damaged the U.S. image overseas by alleging that U.S. interrogators desecrated the Koran at Guantanamo Bay. The May 9 report triggered several days of rioting in Afghanistan and other countries in which at least 16 people were killed. Newsweek's editor, Mark Whitaker, apologized to the victims on Sunday and said the magazine inaccurately reported that U.S. military investigators had confirmed that personnel at the detention facility in Cuba had flushed the Muslim holy book down the toilet. "It's puzzling...