Astronaut Donald R. Pettit would often rig an array of as many as six cameras in the cupola windows and set them all to fire continuously for events such as sunsets, which only last around seven seconds on the ISS. (Photo by Donald R. Pettit)

A boat commutes across the Mekong river in Phnom Penh on August 8, 2014. The Mekong is the world's twelth longest river running from the Tibetan Plateau through China's Yunnan province, Myanmar, Laos, Thailand, Cambodia and Vietnam. (Photo by Tang Chhin Sothy/AFP Photo)

A combination photo shows some of the colourful doors seen in Rabat's Medina and Kasbah of the Udayas, September 2014. UNESCO made Rabat a World Heritage Site two years ago and media and tour operators call it a “must-see destination”. But it seems the tourist hordes have yet to find out. While visitors are getting squeezed through the better-known sites of Marrakesh and Fez, the old part of Rabat - with its beautiful Medina and Kasbah of the Udayas - remains an almost unspoiled oasis of calm. Smaller and more compact, its labyrinths of streets, passages and dead ends are a treasure trove of shapes and colours, of moments begging to be caught by the photographer's lens. (Photo by Damir Sagolj/Reuters)

A Mai-Mai rebel soldier shows off his guns at a checkpoint near the Mugunga refugee camp in Zaire; 1996. (Photo by Carol Guzy/The Washington Post)

Seljalandsfoss waterfall, located in Iceland. Seljalandsfoss is one of the most famous waterfalls of Iceland. This waterfall of the river Seljalandsá drops 60 metres (200 ft) over the cliffs of the former coastline. It's possible to go behind the waterfall. (Photo by HotSpot Media)

A Brazil fan waits for the start of the group A World Cup soccer match between Brazil and Croatia, the opening game of the tournament, in the Itaquerao Stadium in Sao Paulo, Brazil, Thursday, June 12, 2014. (Photo by Felipe Dana/AP Photo)

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)

The Wildscreen festival is the world’s biggest celebration of screen-based natural history storytelling which takes place every two years in Bristol. Here: “Walrus in Midnight Sun”. Walrus feed mostly on bivalves in productive, shallow and often sandy habitats in the Arctic. This individual, though, arrived on a beach outside Tromsø, northern Norway, and found comfort on a stranded dead sperm whale. After two weeks he approached Audun, and only half a metre away he stretched his tusk forward and touched his hand gently. “This was one of the most memorable moments of my life”, Rikardsen says. He named the 500kg male Buddy. After two months, the dead whale was decomposed and Buddy suddenly disappeared. (Photo by Audun Rikardsen/Wildscreen 2016)