“Aurora Hunters”. Photographers taking part in a photography tour on the Lofoten Islands in Norway, pull over on the side of the road to take a photo of their first ever Aurora Borealis after spotting it from their tour bus. Photo location: Rystad, Lofoten Islands, Norway. (Photo and caption by Mark Gee/National Geographic Photo Contest)

Walkers cross the river Waalbrug during the first day of the 98th annual four-days walking event, the “Vierdaagse” in Nijmegen, Netherlands, July 15, 2014. The “Nijmeegse Vierdaagse” is an annual public four-day field march which is held since 1909 in the third week of July. (Photo by Erik van 't Wout/EPA)

Two young boys kneel on stools on either side of a round table as one uses a match to this the other's cigarette, November 12, 1928. (Photo by FPG/Getty Images)

A dog from the K9 Division of the Sri Lanka Army’s Commando Regiment performs during an event to mark International Children’s Day at a school in Welisara, Colombo, Sri Lanka, 01 October 2016. Sri Lanka marks the Children's Day on 01 October with more emphasis on prevention of child abuse. (Photo by M.A. Pushpa Kumara/EPA)

A roadside currency exchange vendor sorts Indian currency notes at his stall in Agartala, India, December 6, 2016. (Photo by Jayanta Dey/Reuters)

Armed forces veteran Frank Simpson at the Portico library being camouflaged by body artist Carolyn Roper in Manchester, UK on May 16, 2016 as part of the #CountThemIn campaign launched on Monday by the Royal British Legion. (Photo by Jon Super/Royal British Legion/PA Wire)

A Bangladeshi girl plays on a swing, in Dhaka, Bangladesh, December 27, 2016. (Photo by Mohammad Ponir Hossain/Reuters)

A woman walks with her child past a Soyuz rocket, installed as a monument at the Russian leased Baikonur cosmodrome, the world's first and largest operational space launch facility, in Baikonur, Kazakhstan, Saturday, November 12, 2016. The new Soyuz mission to the International Space Station (ISS) is scheduled for Friday, Nov. 18. (Photo by Dmitri Lovetsky/AP Photo)