Young man making the O.K. sign. (Photo by George Marks/Retrofile/Getty Images). Circa 1950s

A Bedouin rifleman hides behind his camel while he carefully takes aim in the Sahara desert. (Photo by Three Lions/Getty Images). Circa 1955

Framed by the setting sun, an American Bison grazes at the Tallgrass Prairie National Preserve on Tuesday, April 28, 2015, near Strong City, Kan. The buffalo herd at Tallgrass is one of the few herds of wild bison left in the United States. (Photo by Travis Heying/The Wichita Eagle via AP Photo)

Competitors prepare backstage before the 2015 Brazil Miss and Mister Fitness contest in Sao Paulo, Brazil, June 18, 2015. Some 96 men and women from all across the country competed in the event. (Photo by Paulo Whitaker/Reuters)

Participants of the techno-parade “Zug der Liebe” (Train of love) dance on a street in Berlin, Germany July 25, 2015. The “Zug der Liebe” is the successor to the “Loveparade”, which in its heyday attracted up to 100,000 participants and ended in disaster and tragedy in 2010 when 21 people died and over 500 were injured due to suffocation from overcrowding at the “Loveparade” in Duisburg. (Photo by Axel Schmidt/Reuters)

A comedic photo of a cheetah appearing to find something hilarious by Dutton Robert for the Comedy Wildlife Photo Awards 2016, South Africa, April, 2012. (Photo by Dutton Robert/Barcroft Images/Comedy Wildlife Photo Awards)

A train attendant helps a passenger to adjust her seat at the business class carriage on a CRH 380A bullet train Thursday, June 16, 2011. (Photo by Reuters/China Daily)

People are caught in a dust storm in New Delhi, India May 23, 2016. (Photo by Anindito Mukherjee/Reuters)