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

Self-employed pedicab driver Danilo Guerra, 25, uses his mobile phone as he waits for clients in downtown Havana April 12, 2016. (Photo by Alexandre Meneghini/Reuters)

Negin Ekhpulwak, leader of the Zohra orchestra, an ensemble of 35 women, practises on a piano at Afghanistan's National Institute of Music, in Kabul, Afghanistan April 9, 2016. Playing instruments was banned under Taliban rule in Afghanistan, and even today, many conservative Muslims frown on most forms of music. Living in an orphanage in the capital, Kabul, 19-year-old Negin Ikhpolwak leads an ensemble of 35 women that plays both Western and Afghan musical instruments. In a country notorious internationally for harsh restrictions on women in most areas of life, Negin's story highlights a double challenge. (Photo by Ahmad Masood/Reuters)

Carnival revellers pose during the postponed “Rosenmontag” (Rose Monday) parade in Mainz, Germany, May 8, 2016, after the original parade in February was cancelled due to severe weather. (Photo by Ralph Orlowski/Reuters)

A general view shows smoke and volcanic ashes billowing from volcano Cotopaxi in Pedregal, Ecuador, late 07 October 2015. (Photo by Jose Jacome/EPA)

A vendor drinks water as she waits for customers at a roadside flower market in Ahmedabad, India, February 8, 2017. (Photo by Amit Dave/Reuters)

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)