New York City policemen tangled with demonstrators at a subway station on the opening day of the New York World's Fair, April 22, 1964. Youths attempted to stall the train, which was headed from the city to the fairgrounds, as a form of protest on behalf of civil rights for blacks. (Photo by Charles Gorry/AP Photo)

A Common Blue Morpho butterfly lands on the arm of Garbiella as it and hundreds of other butterflies from around the world fill the bird aviary for the next month at the San Diego Zoo Safari Park in San Diego, California March 13, 2015. Called the Butterfly Jungle, the exhibit has over 30 species of butterflies. (Photo by Mike Blake/Reuters)

A competitor reacts as she emerges from the water during the Tough Guy event in Perton, central England, January 26, 2014. The annual Tough Guy race – “the toughest race in the world” – at Perton in Staffordshire. Tough Guy claims to be the world’s most demanding one-day survival ordeal. First staged in 1987, the Tough Guy Challenge has been widely described as one of the hardest races of it’s type with up to one-third of the starters failing to finish in a typical year. (Photo by Darren Staples/Reuters)

A bride weeps in a mass wedding ceremony at the CheongShim Peace World Center in Gapyeong, South Korea, Wednesday, February 12, 2014. Some 2,500 South Korean and foreign couples exchanged or reaffirmed marriage vows in the Unification Church's mass wedding arranged by Hak Ja Han Moon, wife of the late Rev. Sun Myung Moon, the controversial founder of the Unification Church. (Photo by Lee Jin-man/AP Photo)

China’s new tallest building has received unexpected publicity thanks to Russian free climbers Vadim Makhorov and Vitaly Raskalov. The pair took two hours to climb 650 metres up the unfinished Shanghai Tower. They did not use safety equipment on their ascent to the top of a crane attached to the tower, from where they took these extraordinary pictures of Shanghai. Photo: Vitaly Raskalov's feet dangle from the top of the Shanghai Tower, high above the Shanghai World Financial Centre. (Photo by Vitaly Raskalov/Caters News Agency)

Alex Plunkett, left, and Sean Hart, both of Arlington, Va., join hundreds participating in the annual International Pillow Fight Day on April 5. Massive pillow fights broke out on the Mall in Washington and in cities around the world. (Photo by Marvin Joseph/The Washington Post)

A woman smiles as she gets a new tattoo during Rio Tattoo Week in Rio de Janeiro, Brazil, Friday, January 16, 2015. Tattoo artists from Brazil and around the world gathered for the annual three day convention. (Photo by Silvia Izquierdo/AP Photo)

U.S. players push head coach Adam Krikorian into the pool after they defeated the Netherlands in their women's water polo gold medal match during the Aquatics World Championships in Kazan, Russia, August 7, 2015. (Photo by Michael Dalder/Reuters)