The fourth annual BigPicture Natural World Photography Competition aims to celebrate the diversity of life on Earth, and encourages people to protect and conserve it. Here: “The Salmon Catchers”. Terrestrial Wildlife. To capture this view of a mother grizzly bear and her cub, photographer Peter Mather set up a camera trap on a log that he knew the bears tended to traverse while fishing for salmon, in the Yukon River watershed in Canada. (Photo by Peter Mather/BigPicture Natural World Photography Competition 2017)

A horse pulls a driving school car as other drivers push their vehicles behind during a demonstration by driving instructors in Belgrade, September 25, 1992. Due to gasoline shortage in the Yugoslav capital, driving instructors are staying away from work. (Photo by AP Photo)

“Catch of the Decade”. Can you guess what happened next? Photo location: Katmai National Park, Alaska, USA. (Photo and caption by Aaron Baggenstos/National Geographic Photo Contest)

Participants at the Dubai Run at Sheikh Zayed Road in Dubai, United Arab Emirates on November 26, 2021. (Photo by Ruel Pableo for The National)

A commuter exits a closed off station after a subway train derailment, Tuesday, June 27, 2017, in the Harlem neighborhood of New York. A subway train derailed near a station in Harlem on Tuesday, frightening passengers and resulting in a power outage as people were evacuated from trains along the subway line. The Fire Department of New York said a handful of people were treated for minor injuries at around 10 a.m. It said there was smoke but no fire. Delays were reported throughout the subway system. (Photo by Mary Altaffer/AP Photo)

Tennis star Maria Sharapova poses with a Porsche 911 RSR race car at the 2016 Los Angeles Auto Show in Los Angeles, California, U.S November 16, 2016. (Photo by Mike Blake/Reuters)

This undated handout picture taken by Tim Samuel and provided through his Instagram account shows a small fish swimming inside the belly of a jellyfish off the coast of Byron Bay in New South Wales, eastern Australia. A fish has been pictured swimming inside a jellyfish off Australia's east coast in a remarkable and rare image that has gone viral, with more than two million online views. Underwater photographer Tim Samuel was in the water with a friend near popular tourist resort Byron Bay in December when they came across the little creature trapped inside the only slightly larger jellyfish. (Photo by Tim Samuel Photography/AFP Photo/Instagram)

“Strike Through The Mothership”. Every May for the last 3 years I have driven down to Tornado Alley to capture some amazing storms. This supercell held so much promise to drop a tornado but one small shift in the atmosphere and all that it produced was an extreme lightning show. Photo location: Broken Bow, Nebraska. (Photo and caption by Vanessa Neufeld/National Geographic Photo Contest)