A migrant boy sits on railway tracks at a train station in Tovarnik, Croatia, September 20, 2015. (Photo by Antonio Bronic/Reuters)

Participants run through the streets of the Back Bay during the 16th annual Santa Speedo Run in Boston, Massachusetts, December 12, 2015. (Photo by Brian Snyder/Reuters)

A fighter of Libyan forces allied with the U.N.-backed government runs for cover during a battle with Islamic State fighters in Sirte, Libya, July 31, 2016. (Photo by Goran Tomasevic/Reuters)

In this September 10, 1977, file photo, from left, Hua Guofeng, Chinese Communist Party (CCP) chairman and Mao Zedong's immediate successor; Ye Jianying, CCP vice chairman and future ceremonial head of state; Deng Xiaoping, no formal titles at the time but soon to emerge as paramount leader during the reform era; Li Xiannian, CCP vice chairman and future president; Wang Dongxing, head of the leadership bodyguard unit who helped topple the Gang of Four, view the body of later Chinese leader Mao Zedong in Beijing. (Photo via AP Photo)

Festival goers arrive for the Glastonbury festival at Worthy Farm, in Somerset, England, Thursday, June 23, 2016. (Photo by Guy Bell/Rex Features/Shutterstock)

People take part in the “The Burial of the Sardine” funeral procession, which marks the end of carnival festivities, in Madrid, Spain, February 10, 2016. “Mourners” carry a coffin with a mock sardine through the streets to celebrate the countdown to Lent. Spanish painter Francisco de Goya's painting “El entierro de la sardina” (The Burial of the Sardine) was inspired by this tradition, which started in Madrid in the 18th century, around the time of Spanish King Carlos III. (Photo by Juan Medina/Reuters)

LONDON - JUNE 04: A piece entitled “Entrance into wood” by Elke Krystufek goes on show at The Royal Academy Summer Exhibition on June 4, 2008 in London. In it's 240th year, the exhibition displays a wide range of recent work by both established and emerging artists. 10,000 artists submitted work for selection this year. (Photo by Peter Macdiarmid/Getty Images)

Egyptian bootblacks cleaning a European's shoes in Cairo. (Photo by Hulton Archive/Getty Images). Circa 1870