A dejected German Grenadier carrying a machine gun on his shoulder in front of a building on fire during the German retreat in Russia. (Photo by Keystone/Getty Images). 1944

Eight-year-old Niu Dongfang trains at the No. 2 Beijing Shuangqiao School January 13, 2005 in Beijing, China. Most of students in the gymnastics school have to study more than five years from as young as age six before they become athletes. (Photo by Guang Niu/Getty Images)

Revellers, dressed as “Zarramaches”, pose inside the city hall during celebrations to mark Saint Blaise's festivity in Casavieja, Spain February 3, 2017. (Photo by Sergio Perez/Reuters)

Damselflies covered in dew rest on a wild flower by the Po River, northern Italy on August 15, 2016. (Photo by Alberto Ghizzi Panizza/Barcroft Images)

Body modification and tattoo artist Andrea Aguilar, 26, known as leopard woman, at the Quito Tattoo Convention shows off her work during the last day of the event in Quito, Ecuador September 27, 2015. (Photo by Guillermo Granja/Reuters)

With their wings at full length, these beautiful golden eagles soar through the skies in a glorious training session to hunt their prey. Others sit on the arms of their owners and trainers. Batzaya Choijiljav, 41, from Mongolia has taken these magnificent pictures at the annual traditional Kazakhs festival, October 2015. (Photo by Batzaya Choijiljav/Caters News)

The Vietnam Slide Project was created by photo editor Kendra Rennick, who began collecting photo slides after a close friend lost her father, a Vietnam veteran. Her friend found a box of slides that her father had taken while in Vietnam and from there Rennick has continued to collect photographs that Vietnam veterans took during their tours of duty. Here: A photo taken from the collection of D.Thornton, who served in the First Air Cavalry division of the United States Army. (Photo by D.Thornton/The Vietnam Slide Project)

A competitor solves a Rubik's cube using his feet as he prepares for the Rubik's Cube European Championship in Prague, Czech Republic, July 15, 2016. (Photo by David W. Cerny/Reuters)