A photographer tested the concentration of several pairs of dogs as he captured their reactions to treat time in a series of shots. Christian Vieler, 47, of Waltrop, Germany, has been a professional dog photographer since 2016. He came up with the idea of snapping two dogs catching treats simultaneously. Here: Basset Hounds. (Photo by Vieler Photography/Caters News Agency)

Russian pop art photographer Sergey Chilikov captures a nation liberated from the social oppression of late-era Soviet rule – at parties, in the streets, and bouncing high. His exhibition, Photoprovocations, will be at Photo London, 19-22 May. Here: Yoshkar-Ola, Matrosova Street (1995). (Photo by Sergey Chilikov)

Unforgiving temperatures of up to 60℃ (140℉) beat down on these saltminers on a daily basis. The mines, situated in the Afar Triangle in Ethiopia, stretch across 38,000 sq miles and at their lowest point are more than 300ft below sea level. Joel Santos travelled to capture the area’s dry, brutal beauty. Here: Dromedaries and donkeys are used to transport the salt. (Photo by Joel Santos/Barcroft Images)

Lioness and hyena posture to one another, in Masai Mara, Kenya, August 2015. A photographer captured one of the oldest rivalries in the animal kingdom as a pair of lions went head to head with a pack of hungry hyenas. (Photo by Ingo Gerlach/Barcroft Images)

Ten finalists capture the theme of “through young eyes” in this young photographers’ competition that aims to engage youth around the world in wildlife conservation. Here: Heavy bodied jumping spider by Md Rashuidul Rabby, age 23, from Bangladesh. (Photo by Md Rashuidul Rabby/WWD2017)

“Sperm whale opening it's huge mouth, Ogasawara Islands, Japan. Sperm whales are the biggest carnivorous animals on the planet. Each teeth in the mouth of adult specimen weights more than 1 kilogram. Interestingly enough that modern marine biologists believe that these teeth despite being fearsome play little role in capturing and eating giant squid – with their main function being mainly ritual aggression between males!”. (Photo by Alexander Safonov)

A member from the Iraqi security forces beats an Islamic State insurgent, who was captured in Tikrit April 1, 2015. Iraqi troops and Shi'ite paramilitary fighters were battling Islamic State on Wednesday in northern Tikrit, which officials described as the Sunni Muslim militant group's last stronghold in the city. (Photo by Alaa Al-Marjani/Reuters)

The Perth-based photographer and journalist Frances Andrijich has travelled the Western Australian coast since the early 90s, capturing clotheslines in all their glory. In her images they take the roles of play equipment, Christmas trees and, in the summer, a homemaker’s dream. Andrijich admits she is hopelessly hung up on clotheslines; her latest book celebrates them under the spotlight of the Australian sun. Here: Vera Germanis hangs out underwear in Frances Andrijich’s grandparents’ backyard. This was the photographer’s first clothesline shot, taken in Midland Junction in 1991. (Photo by Frances Andrijich)