An ancient oak tree sits in a Shropshire field as the first signs of Spring begin to show across the United Kingdom on February 19, 2014 in Bridgnorth, England. (Photo by Christopher Furlong/Getty Images)

A woman sits with a Great Dane during the first day of the Crufts dog show in Birmingham, central England March 6, 2014. (Photo by Darren Staples/Reuters)

Soviet Army soldiers sit on their tanks in front of the Czechoslovak Radio station building in central Prague during the first day of Soviet-led invasion to then Czechoslovakia on August 21, 1968. (Photo by Libor Hajsky/Reuters)

The contest began in 2007, and since then photographers from more than 70 countries have entered. Photo: Michael O'Neal of San Francisco won first place in the animals category in the 2014 iPhone Photography Awards. (Photo by Michael O'Neal)

A man sleeps on a wheelbarrow outside a closed shop at a market during the first day of a ceasefire in Yemen's capital Sanaa April 11, 2016. (Photo by Khaled Abdullah/Reuters)

A wild cow jumps over revelers in the bullring after the first running of the bulls at the San Fermin festival in Pamplona, northern Spain, July 7, 2016. (Photo by Eloy Alonso/Reuters)

Gas-masked men of the British Machine Gun Corps with a Vickers machine gun during the first battle of the Somme, 1916. (Photo by General Photographic Agency/Getty Images)

Cheerleaders let their hair fly as they perform prior to a German first division Bundesliga soccer match between 1. FC Cologne and Bayern Munich in Cologne, Germany, March 4, 2017. (Photo by Michael Probst/AP Photo)