Fighters of the Free Syrian Army fire an anti-aircraft weapon in the rebel-held Mashhad area in southeastern Aleppo, on December 12, 2016, as they battle Syrian government forces during an operation to retake the embattled city. The crucial battle for Aleppo entered its “final phase” after Syrian rebels retreated into a small pocket of their former bastion in the face of new army advances. The retreat leaves opposition fighters confined to just a handful of neighbourhoods in southeast Aleppo, the largest of them Sukkari and Mashhad. (Photo by AFP Photo/Stringer)

A Free Syrian Army fighter walks past a flag of al-Furqan brigade as a rifle hangs from a branch in the orchards of Kafar Zita in Hama countryside January 22, 2015. (Photo by Mohamad Bayoush/Reuters)

A Rohingya refugee woman is helped from a boat as she arrives exhausted on the Bangladesh side of the Naf River at Shah Porir Dwip after fleeing her village in Myanmar, on October 1, 2017 in Cox's Bazar, Bangladesh. (Photo by Kevin Frayer/Getty Images)

Children react after what activists said was shelling by forces loyal to Syria's President Bashar al-Assad near the Syrian Arab Red Crescent center in the Douma neighborhood of Damascus May 6, 2015. (Photo by Bassam Khabieh/Reuters)

A traveller washes his horse in the River Eden in preparation for selling at the Appleby Horse Fair on June 3, 2011 in Appleby, England. Appleby Horse Fair has existed under the protection of a charter granted by James II since 1685. It is one of the key gathering points for the Romany, gypsy and traveling community. Appleby Horse Fair is attended by about 5,000 travelers who come to buy and sell horses. The animals are washed and groomed before being ridden at high speed along the “mad mile” for the viewing of potential buyers. (Photo by Christopher Furlong/Getty Images)

Long-tailed mayflies (Palingenia longicauda) at Tisza river near Tiszainoka 135km (84 miles) southeast of Budapest, June 23, 2013. Millions of these short-lived mayflies engage in a frantic rush to mate and reproduce before they perish in just a few hours during “Tiszaviragzas” or Tisza blooming season from late spring to early summer every year. (Photo by Laszlo Balogh/Reuters)

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

A child plays with a soap bubble on the city hall plaza on March 14, 2015 in Paris. (Photo by Dominique Faget/AFP Photo)