Mounted cop in action on Tremont Street in Boston, Massachusetts, 1920 – 1929 (approximate). (Photo by Leslie Jones)

Neil Zeller's snaps were taken across Canada, where he photographs the northern lights dancing across a dark night sky. In one stunning shot, Zeller, 42, even manages to capture a flash of lightning beneath a storm cell while an aurora gives off a magnificent green glow. The photographer, from Calgary, Alberta, describes himself as a night person, and became interested in night photography about 10 years ago. (Photo by Neil Zeller/Caters News)

Three Boeing 737 fuselages lie on an embankment on the Clark Fork River after a BNSF Railway Co train derailed Thursday near Rivulet, Montana in this picture taken July 4, 2014. A train derailment in Montana this week damaged a shipment of jetliner fuselages and other large parts on its way to Boeing Co factories in Washington state from Spirit Aerosystems, Boeing said on Saturday. (Photo by Kyle Massick/Reuters)

Photos of Edward Snowden, a contractor at the National Security Agency (NSA), and U.S. President Barack Obama are printed on the front pages of local English and Chinese newspapers in Hong Kong in this illustration photo June 11, 2013. Snowden, who leaked details of top-secret U.S. surveillance programs, dropped out of sight in Hong Kong on Monday ahead of a likely push by the U.S. government to have him sent back to the United States to face charges. (Photo by Bobby Yip/Reuters)

A man and his dog wade through a flooded road in Vila Velha, Espirito Santo state, Brazil, on December 27, 2013. At least 44 people have died and more than 60,000 have been left homeless following torrential rains over the past few weeks in southeast Brazil. (Photo by Yasuyoshi Chiba/AFP Photo)

In this Tuesday, February 11, 2014, photo, a trained monkey, that makes a living for her Pakistani owner by performing to a crowd in public and private places, sits held by a leash, in Rawalpindi, Pakistan. For Pakistanis who raise and train the monkeys they are an important source of income in an impoverished country, and they form a strong bond with the animals. The monkeys are usually captured in the wild when they are babies and then trained. A trained monkey can fetch 20,000 to 30,000 rupees ($190 to $285). (Photo by Muhammed Muheisen/Associated Press)

Festival goers run toward the main stage to catch the beginning of Kendrick Lamar's set during the first weekend of Coachella 2012, on April 13, 2012. (AP Photo/Chris Pizzello)