In this March 13, 2015 photo, Yohan, 4, from left, Cristian, 7, and Angelo, 6, playfully toss coca leaves into the air, singing: “I have a lot of money, look at all the money I have”, in La Mar, province of Ayacucho, Peru. Hauling cocaine out of the remote valley is about the only way to earn decent cash in this region where a farmhand earns less than $10 a day. Beyond extinguishing young lives, the practice has packed Peru's highland prisons with cocaine backpackers while their bosses evade incarceration. (Photo by Rodrigo Abd/AP Photo)

In this artist's impression supplied by the ESO (European Southern Observatory) on April 25, 2007, the planetary system around the red dwarf, Gliese 581, is pictured showing what astronomers believe is the most earth like planet found outside our solar system to date. Using the ESO 3.6-m telescope in Chile, astronomers have uncovered the planet which could have water running on its surface. The planet orbits the faint star Gliese 581, which is 20.5 light-years away in the constellation Libra. (Photo by ESO via Getty Images)

Do tears of joy look the same as ones of woe—or ones from chopping onions? In “The Topography of Tears,” the Los Angeles-based photographer Rose-Lynn Fisher explores the physical terrain of one hundred tears emitted during a range of emotional states and physical reactions. Using a Zeiss microscope with an attached digital camera, she captures the composition of tears enclosed in glass slides, magnified between 10x and 40x. “There are many factors that determine the look of each tear image, including the viscosity of the tear, the chemistry of the weeper, the settings of the microscope, and the way I process the images afterwards,” she says.

Beneath the Swedish capital lies an intricate web of underground train lines. More than 90 of the 100 stations in the 110km tunnel system, sometimes referred to as “the world’s longest art gallery”, have been decorated with paintings, installations, mosaics and sculptures by 150 artists since the 1950s. After spending a couple of weeks exploring arctic Norway and Sweden, London-based travel photographer Conor MacNeill headed underground to capture images of the metro stations. Here: A rainbow arcs over a girl on the platform of Stadion station. (Photo by Conor MacNeill/The Observer)

Photographer Joana Choumali’s latest project explores body image and beauty by documenting the men building Abidjan’s clothing models. The “Awoulaba” mannequin is a customised model designed with the African ideal of beauty in mind, curvier than the stick-thin examples usually seen in the west. They first appeared in 2011, and have since become a familiar sight outside the numerous clothing shops dotted throughout Ivory Coast’s capital, Abidjan. Here: An apprentice lines up his work on a roadside. (Photo by Joana Choumali)

Vogue Italia is hosting a series of shows in Milan exploring how the magazine seeks to engage with hot social and political issues and provoke debate through images by top photographers. The Photo Vogue festival in Milan is hosting three exhibitions. The first, Fashion and Politics in Vogue Italia, looks at the magazine’s ambition to be a catalyst for change – in subtle and playful ways. Here: David LaChapelle – October 2004. (Photo by David LaChapelle/The Guardian)

Three pugs peer out from a car window in Los Angeles, California. A wacky photographer has come up with an unusual pet project – snapping ecstatic dogs as they hang their heads out of car windows. Lara Jo Regan, 48, embarked on the odd task for her new 2014 calendar “Dogs In Cars”. The unusual shoot, which took place in Los Angeles, California, aimed to explore the joy experienced by pugs and huskies when a breeze hits their faces. (Photo by Lara Jo Regan/Barcroft Media)

Children sit under a crocodile based table, as they pose for photographers during a press preview of a themed auction that features the animal as artistic inspiration, entitled “Creatures Great and Small”, in London, Monday, December 15, 2014. The sale scheduled for December 17, 2014, explores animals across a diverse range of mediums and styles, from intricate carving details in 19th century furniture through to contemporary sculpture, according to Christie’s auction house. (Photo by Lefteris Pitarakis/AP Photo)