A leopard seal feeds Paul Nicklen a penguin. (Photo by Paul Nicklen/National Geographic). Antarctic Peninsula, 2011

A police officer removes a reveler from standing on a post as they guard and clear the street of revelers dressed in holiday themed costumes during SantaCon in New York Saturday, December 12, 2015. As thousands of Santa-suited merrymakers prepare to hit the city's streets and bars, organizers of the annual pub crawl say they're taking more steps than ever to deter naughty behavior. (Photo by Andres Kudacki/AP Photo)

A recruitment drive during the First World War at Trafalgar Square, London. (Photo by Central Press/Getty Images)

The Lumix GX1 single lens reflex (SLR) camera with 14-42 mm powerzoom lens is displayed at the Panasonic booth at the 2012 International Consumer Electronics Show at the Las Vegas Convention Center January 10, 2012 in Las Vegas, Nevada. The new camera comes with an external viewfinder and flash and an ISO up to 12,800. The camera as shown sells for USD 949; the camera body alone is USD 799. (Photo by Ethan Miller/Getty Images)

Looking towards the Times Building on Times Square, the Paramount Building is on the right, and Seventh Avenue on the left crossing Broadway. (Photo by General Photographic Agency/Getty Images). Circa 1930

A Russian trenchmortar crew run to take up a new firing position in the Stalingrad area during the Great Patriotic War. (Photo by Keystone/Getty Images). October 1942

Students from Glasgow Art School modelling casual clothing and Buchan tartan in the annual Fashion Show for charities. During Rag Week students parade in the city streets wearing costumes designed and made by themselves. (Photo by Haywood Magee/Picture Post/Getty Images). 7th February 1953

Three Chinese soldiers at the time of a civil war in China. (Photo by General Photographic Agency/Getty Images). 1922