A policeman kick in the door of a residence next to the Black Panther headquarters in New Orleans as they moved in following a shootout, September 15, 1970. Other heavily armed policemen stand at ready. (Photo by Jack Thornell/AP Photo)

A young Chinese girl dressed in Christmas costume, hugs a pedestrian on a street to celebrate Christmas in Nanjing city, east China's Jiangsu province, 23 December 2015. (Photo by Imaginechina/Splash News)

A man prays to mourn victims of the March 11, 2011, earthquake and tsunami in front of a ship brought ashore by the disaster in Kesennuma, Miyagi Prefecture, Japan. (Photo by Kyodo via Reuters)

A guard stands at Dityatki checkpoint, marking a 30 km (18-mile) zone around the Chernobyl nuclear power plant April 23, 2013. Ukraine will mark the 27th anniversary of the Chernobyl disaster, the world's worst civil nuclear accident, on April 26. (Photo by Gleb Garanich/Reuters)

Members of the Women's Fire Brigade with their Chief Officer, March 1916. (Photo by Topical Press Agency)

Boeing B-29 (#10) from the 24th Bomb Squadron, 6th Bomb Group after an emergency landing at Iwo Jima on April 24,1945. (Photo by U.S. Air Force)

The Pink Floyd inflatable pig floats next to Broadcasting House to promote their new exhibition at the V&A museum, in London, Britain May 10, 2017. (Photo by Neil Hall/Reuters)

A group of colorful row houses are reflected on to the top of a black car parked on 3600 block of N street in the Georgetown section of Washington DC, February 16, 2017. (Photo by John McDonnell/The Washington Post)