People take pictures with their mobile phone of a scale model of a dinosaur displayed in front of La Sapienza University headquarters in Rome April 10, 2015. The realistic reproductions of dinosaurs are part of the “Dinosaurs in the flesh, science and art bring to life the rulers of a lost world” exhibition. (Photo by Alessandro Bianchi/Reuters)

“Winter Climbing from inside Ben Nevis”. The view from inside the mountain, as a winter climber passes through the cave on Minus Three gully. Photo location: Ben Nevis, Fort William, Scotland. (Photo and caption by Daniel Wildey/National Geographic Photo Contest)

Spacewalker Mark Vande Hei took his own photograph during the first spacewalk of 2018, on January 23, 2018. These sky-high pictures are better known as “space-selfies”. (Photo by Mark Vande Hei/NASA)

A U.S. Marine kneels beside a Multi-Utility Tactical Transport ( MUTT) during a patrol as part of Rim of the Pacific (RIMPAC) 2016 an exercise held at Camp Pendleton, California United States, July 13, 2016. (Photo by Mike Blake/Reuters)

A woman poses for a picture taken by her friend (not in picture) in a temple decorated to celebrate Chinese New Year at Samut Prakan province outside Bangkok February 7, 2016. (Photo by Jorge Silva/Reuters)

The Jet Propulsion Lab team's RoboSimian robot turns on a valve at a simulated disaster-response course during day one of the Defense Advanced Research Projects Agency (DARPA) Robotics Challenge finals in Pomona, California, June 5, 2015. (Photo by David McNew/Reuters)

Participants take pictures of themselves as others run past the Tiananmen gate during the Beijing Marathon in Beijing, China, September 17, 2016. (Photo by Damir Sagolj/Reuters)

Convicted murderer Hector Alvarado Mazariegos, right, drops to the ground as he is hit by bullets of a Guatemala firing squad in the public cemetery at Mazatenango, June 28, 1975. His companion, Rocael Ortiz, met the same fate a few seconds later. Both were convicted of murder. (Photo by AP Photo/Anzueto)