Clouds gather as walkers pause atop a ridge in Mountain View, California January 7, 2016. (Photo by Noah Berger/Reuters)

A neighborhood watch volunteer stands guard on her street on February 9, 2017 in Peronia, Guatemala. Residents of Peronia, south of Guatemala City organized block by block to secure their community after ten of their neighbors in January were killed, they say, for refusing to pay extortion money to gangs. Armed with machetes and sticks, residents take turns each night, baring strangers' entry into their neighborhoods. Violence and poverty continue to drive emigration from Central America to the United States, even as the Trump administration moves to tighten border security. (Photo by John Moore/Getty Images)

A policeman stands by a burning car, set alight during a communist march in the East End of London. (Photo by Topical Press Agency/Getty Images). Circa 1936

A Ugandan soldier, part of the 9,000-strong African Union Mission in Somalia, (AMISOM) walks through the Banadir soccer stadium on August 15, 2011 in Mogadishu, Somalia. The stadium, Somalia's largest soccer facility, had been under control by Islamic extremist Shabab militants for the past two years until they withdrew from the capital more than a week ago. (Photo by John Moore/Getty Images)

Father Christmas waiting for a bus in the London West End with his reindeer and a sack of presents. (Photo by Evening Standard/Getty Images). 12th August 1970

Bad Christmas gift makes the pretty girl look disappointed in x-mas time under the christmas tree. (Photo by pixelrain/Rex Features/Shutterstock)

Palestinians walk on a road during a power cut in Beit Lahiya in the northern Gaza Strip January 11, 2017. (Photo by Mohammed Salem/Reuters)

People ride a prototype of a driverless vehicle as it is moves through a pedestrian area in Greenwich, east London, February 11, 2015. Britain has begun testing driverless cars in four cities, launching the first official trials ahead of a series of planned rule reviews to accommodate the new technology. (Photo by Suzanne Plunkett/Reuters)