An Indian woman collects camel dung during the annual cattle fair in Pushkar, in the western Indian state of Rajasthan, Sunday, November 10, 2013. Pushkar, located on the banks of Pushkar Lake, is a popular Hindu pilgrimage spot that is also frequented by foreign tourists who come to the town for the annual cattle fair and camel races. (Photo by Ajit Solanki/AP Photo)

Harris & Ewing Inc. photographed people, events, and architecture, particularly in Washington, D.C., during the period 1905-1945. Photo: Tests of Curtiss Palne for Army, Single Control. Created by Harris & Ewing. Published in 1912.

The main church in the town of San Damian Texoloc, Mexico stands in front of the Popocatepetl volcano as is spews ash and vapor early Tuesday, July 9, 2013. Last Saturday, Mexico's National Center for Disaster Prevention raised the volcano alert from Stage 2 Yellow to Stage 3 Yellow, the final step before a Red alert, when possible evacuations could be ordered after the Popocatepetl volcano spit out a cloud of ash and vapor 2 miles (3 kilometers) high over several days of eruptions. (Photo by J. Guadalupe Perez/AP Photo)

The “Yama” (Pit) memorial is seen in the centre of Minsk May 5, 2015. The memorial is dedicated of the destruction of the Minsk ghetto during World War Two, when several hundred thousands of Jews were slaughtered. Belarus will mark Victory Day on May 9, the 70th anniversary of the Soviet Union's victory over Nazi Germany. (Photo by Vasily Fedosenko/Reuters)

People look at a man, who residents said was killed by al Qaeda militants, hanging on a bridge in Yemen's southeastern city of Mukalla June 17, 2015. Al Qaeda militants in Yemen killed two alleged Saudi spies, residents said, accusing them of planting tracking devices which enabled the assassination of the group's leader in a suspected U.S. drone strike. (Photo by Reuters/Stringer)

A U.S. Army soldier with the 10th Special Forces Group and his military working dog jump off the ramp of a CH-47 Chinook helicopter from the 160th Special Operations Aviation Regiment during water training over the Gulf of Mexico as part of exercise Emerald Warrior 2011 on March 1, 2011. (Photo by Tech. Sgt. Manuel J. Martinez/U.S. Air Force)

The sun rises beside St Mary's Lighthouse in Whitley Bay, Tyne and Wear, as the unseasonably cool weather continues on Thursday, April 28, 2016. (Photo by Owen Humphreys/PA Wire)

A quartet of showgirls in costume sit at an outdoor table and drink from mugs at Disneyland amusement park, Anaheim, California, 1955. (Photo by Loomis Dean/The LIFE Picture Collection/Getty Images)