Riot security forces clash with demonstrators as a motorcycle is set on fire during a protest against Venezuelan President Nicolas Maduro's government in San Cristobal, Venezuela May 29, 2017. (Photo by Carlos Eduardo Ramirez/Reuters)

A little girl holding her newborn sister waits for their turn in a queue during a vaccination campaign under the supervision of the Syrian Arab Red Crescent (SARC) humanitarian nonprofit organization, in the besieged Syrian town of Douma, Syria, 23 May 2017. According to a statement from SARC, in the city of Douma some 12,809 children under the age of five were immunized in a vaccination campaign to prevent measles and poliomyelitis. The campaign was the first of its kind with the participation of 100 volunteers. SARC has been delivering vaccines to 17 health centers approved for vaccination campaigns in towns and villages in the Eastern Ghouta area. (Photo by Mohammed Badra/EPA)

It’s enough to make your head spin. The photographer Katherine Young set out to shoot spiral staircases in London, England to great effect, including this shot she calls the Downward Spiral Part III. (Photo by Katherine Young/Rex Features/Shutterstock)

In this May 14, 2016 photo, children wearing their school backpacks climb on a cliff using a bamboo ladder on their way home from school in Zhaojue county, southwest China's Sichuan province. A village in China's mountainous west where schoolchildren must climb an 800-meter (2,625-foot)-high bamboo ladder secured to a sheer cliff face may get a set of steel stairs to improve it's safety. (Photo by Chinatopix via AP Photo)

Tourists use a selfie stick on the Trocadero Square, with the Eiffel Tower in background, in Paris, Tuesday, January 6, 2015. Selfie sticks have become popular among tourists because you don't have to ask strangers to take your picture, and you can capture a wide view in a selfie without showing your arm. But some people find selfie sticks obnoxious, arguing that they detract from the travel experience. (Photo by Remy de la Mauviniere/AP Photo)

Juri Mitomi, 20, holds a cigarette after a Coming of Age Day celebration ceremony at an amusement park in Tokyo January 12, 2015. According to a government announcement, more than 1.2 million men and women who were born in 1994 marked the coming of age this year, an increase of approximately 50,000 from last year. The increase is also the first since 1995. (Photo by Yuya Shino/Reuters)

Iran's Hanieh Rajabi performs during the women's Daoshu competition at the 13th Wushu World Championships in Jakarta, Indonesia, Monday, November 16, 2015. (Photo by Tatan Syuflana/AP Photo)

A truck carrying iron ore moves along a road at the Fortescue Metals Group (FMG) Christmas Creek iron ore mine located south of Port Hedland in the Pilbara region of Western Australia, November 17, 2015. (Photo by Jim Regan/Reuters)