In Omdurman, the largest city in Sudan, the Qadiriyya Sufi order meets every Friday outside Sheikh Hamed Al Nil mosque, which houses the tomb of their 19th century Sufi leader. (Photo by Ala Kheir, John Burns and Ibrahim Algrefwi/Brownbook)

Men slicing blubber off a large, dead whale. (Photo by Topical Press Agency/Getty Images). Circa 1912

A couple dance tango for tourists at Caminito, a touristic hotspot of La Boca neighborhood in Buenos Aires, Argentina, October 15, 2016. (Photo by Enrique Marcarian/Reuters)

This photo of an elephant seal and Gentoo penguin shot by Andrew James in Yankee Harbour, Antarctica. (Photo by Andrew James/Travel Photographer of the Year)

Hermes Cifuentes, who is also known as “Brother Hermes”, performs an exorcism on Marleny Munoz, 55, who claims to be possessed by spirits in La Cumbre, Valle July 7, 2012. Cifuentes says he has performed more than 35,000 exorcism rituals in the past 25 years. (Photo by Jaime Saldarriaga/Reuters)

Train attendants take part in a parade training as they visit the national flag guard during a patriotic education event ahead of the 90th anniversary of the founding of the Chinese People's Liberation Army (PLA) in Beijing, China July 25, 2017. (Photo by Reuters/China Stringer Network)

In this November 30, 2017 photo, Douglas scoops up mud from the bottom of the polluted Guaire River, in search of gold and anything valuable he can sell, in Caracas, Venezuela. Some stretches of the river smell of sewer while others emit a toxic odor of fuel, a stench that stays in ones nose for hours after leaving the water. (Photo by Ariana Cubillos/AP Photo)

Immigrants from the West Indies at Victoria Station in London, 1956. (Photo by Hulton-Deutsch Collection/CORBIS/Corbis via Getty Images)