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)

An Egyptian security guard screams at people as medics bring in a stretcher to carry the wounded after the attack which killed President Anwar Sadat, October 6, 1981, as he watched a military parade. (Photo by AP Photo)

Cameron Shonnard backflips a jump at Squaw Valley in Olympic Valley, California, December 5, 2015. An El Nino is forecasted for California, and regular precipitation has been welcomed after years of drought. (Photo by Max Whittaker/Reuters)

“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)

Savita, a street performer, helps her dog to balance on empty tin containers as they perform at a roadside in Ahmedabad September 7, 2014. (Photo by Amit Dave/Reuters)

Swimmers in fancy dress splash as they participate in the New Year's Day Loony Dook swim at South Queensferry, Scotland January 1, 2015. (Photo by Russell Cheyne/Reuters)

Models present creations from the Emporio Armani Fall/Winter 2024/2025 collection during Fashion Week in Milan, Italy on February 22, 2024. (Photo by Alessandro Garofalo/Reuters)

The extremely rare Kelvin-Helmholtz cloud formation lurking in the skies over Northumberland in North East England on December 5, 2023. The distinctive formation gets its name from scientists Lord Kelvin and Hermann von Helmholtz who studied the physics behind the rare cloud. (Photo by Ian Davison/South West News Service)