This picture taken on February 23, 2014 shows participants wearing dresses running half-naked in the annual 3.5 km Undie Run held in the Olympic Forest Park smog-covered Beijing. Some 200 participants took part in this event, many of them with gas masks, as dangerous smog blighted swathes of northern China in recent days. (Photo by AFP Photo/STR)

A leopard seal feeds Paul Nicklen a penguin. (Photo by Paul Nicklen/National Geographic). Antarctic Peninsula, 2011

This greedy piglet was isolated from the rest of its litter by the farmer who named it Hitler after it tried to grab all the food at feeding time. (Photo by R J Lewis/Getty Images). 1942

Since 2003, photographer Sergey Fomin has been shooting Russia’s most attractive natural, historical, and architectural objects from different aircrafts. Photo: “An Explosive Scene”. The 1,486-meter-high Karymskii Volcano in Kamchatka. (Photo by Sergey Fomin)

A heat-stressed koala waits as a resident pours water on its back on December 19, 2015 in Adelaide, Australia. Adelaide is experiencing an extreme heatwave, with temperatures reaching over 40 degrees for five consecutive days. (Photo by Morne de Klerk/Getty Images)

Touching and dramatic portraits and landscape shots have won prizes at Australia's prestigious photography prize. Photo: Winner of the NSW (New South Wales) prize: Peter Solness said: “I wanted to re-imagine the lost waterways, so I got my light-painting tools to work. In this image, water is being released from the top of the historic Centennial Park No. 2 Reservoir, which was built in 1925 and holds 90 megalitres of water. After 89 years of incarceration these waters now run free!”. (Photo by Peter Solness/Head On)

These little grizzly bear cubs had fun making a real splash when their mum took them for a dip to learn how to fish. Kamchatka, Russia. (Photo by Marco Mattiussi/Solent News & Photo Agency)

Judy, a black collie whose owner was killed by a train when trying to retrieve her after she slipped her lead. (Photo by Evening Standard/Getty Images). 17th December 1976