A visitor stands in front of a portrait taken by artist Bruce Gilden at the “Masters of Photography” exhibition at the Photokina trade fair in Cologne on September 20, 2016. The fair for the photographic and imaging sector, that is running from September 20 to 25, 2016, presents products from image capture, image processing and storage to image output. Photokina also includes a program of events with congresses, workshops, symposiums and photography exhibitions. (Photo by Patrik Stollarz/AFP Photo)

People ride bicycles in Halloween costumes during “Bike Kill 13” in the Brooklyn borough of New York City, October 29, 2016. “Bike Kill” is an annual gathering of builders and riders of home-made bicycles that culminates in a tall bike jousting competition. (Photo by Stephanie Keith/Reuters)

People take part in a Halloween street party at Lan Kwai Fong on October 31, 2016 in Hong Kong. Halloween, a contraction of All Hallows' Evening, falls on the day before All Saints' Day on November 1, a holiday when Christians remember their deceased loved ones. (Photo by Lam Yik Fei/Getty Images)

A girl carries a rifle as she attends a rally by followers of the Shi'ite Houthi movement commemorating the death of Imam Zaid bin Ali in Sanaa, Yemen October 26, 2016. (Photo by Khaled Abdullah/Reuters)

A participant plays a game on her phone as others watch during a break in a traditional Chinese opera competition at the National Academy of Chinese Theatre Arts in Beijing, China, November 26, 2016. (Photo by Thomas Peter/Reuters)

Purev and Buyantogtokh enjoy the warmth of the fire in the snow in Altai Mountains, Mongolia, September 2016. Navigate the snowy wilds of Mongolia with this nomadic reindeer herding family. Photographer Joel Santos dived 1000km into the depths of Northern Mongolia to visit the Ganbaa family near Khovsgol Lake. (Photo by Joel Santos/Barcroft Images)

Revelers celebrate during fireworks marking the start of the New Year on Copacabana beach on January 1, 2017 in Rio de Janeiro, Brazil. Brazilian revelers traditionally dress in white to honor the New Year's holiday along with the Brazilian Goddess of the Sea- Iemanja. (Photo by Mario Tama/Getty Images)

Local villagers ride a local coal powered steam train on March 27, 2015 at a station in the town of Shixi , Sichuan Province, in Southern China. While China boasts the world's most extensive high-speed rail infrastructure with over 16,000 kilometers of track, the Shixi-Bagou railway is still a primary connection for local villagers between towns and is kept alive by tourist cars carrying passengers for ten times the price. The rail line came into service in the late 1950s and the train was initially used to transport coal from a now-shuttered mine before passenger carriages were added. (Photo by Kevin Frayer/Getty Images)