Pedestrians cover their face as they walk along the dusty road in Kathmandu, Nepal February 27, 2017. Nepal has forced 2,500 old vehicles off roads in its capital city of Kathmandu, part of a fight against alarming air pollution levels that have hit nine times World Health Organisation (WHO) limits. Air pollution has been a chronic problem in rapidly growing Kathmandu, which sits in a Himalayan valley and is home to more than 3mn people. (Photo by Navesh Chitrakar/Reuters)

Tsar Alexander II (1818–1881) known as “The Liberator” lying in state. He was mortally wounded by an assassination attack in St Petersburg. (Photo by Hulton Archive/Getty Images). March 1881

Public Space series, 2015. This series by Morteza Niknahad and Behnam Zakeri tends toward cinema, taking an almost cartoonish view of modern life in Iran. This work was inspired by the social life of dolphins. (Photo by Morteza Niknahad and Behnam Zakeri/The Guardian)

Raising a flag over the Reichstag is a historic World War II photograph taken during the Battle of Berlin on 2 May 1945, by Yevgeny Khaldei.

A rebel fighter supporter shoots an AK-47 rifle as she reacts to the news of the withdrawal of Libyan leader Muammar Gaddafi's forces from Benghazi March 19, 2011. The conflict was sparked by clashes in Benghazi and escalated into a rebellion that spread across the country. Gaddafi was captured and killed on October 20, 2011. Libya is currently caught up in a conflict between two rival factions who once battled together against the late Libyan leader. (Photo by Goran Tomasevic/Reuters)

A guest poses for photographs at the infinity pool of the newly-inaugurated Dolce Hanoi Golden Lake hotel, the world's first gold-plated hotel, in Hanoi on July 2, 2020. It even has a gold-plated infinity pool on the roof. The 400-room, 25-storey property will operate under the American Wyndham Hotels brand. Prices start at $300 a night for rooms, or there are apartments to rent costing from $6400 per square metre. (Photo by Manan Vatsyayana/AFP Photo)

Secondary school students perform a barefoot “pilgrimage of suffering” to support the Occupy Central civil disobedience movement at the Admiralty protest site in Hong Kong November 30, 2014. It has been two months since police first fired tear gas to disperse demonstrators from the main protest site in the Admiralty district next to government offices in the heart of the Asian financial centre. (Photo by Bobby Yip/Reuters)