Vivian Odhiambo, 24, frys samosas in the trading centre of Kogelo, west of Kenya's capital Nairobi, July 14, 2015. Odhiambo said, “Obama is our hero and we wait to welcome him back home again. We in Kogelo have witnessed general growth and we are proud of being associated with the Obamas”, she added. As U.S. President Barack Obama visits Kenya, a personal connection to his father's birthplace of Kogelo dominates a trip that Kenyans view as a native son returning home. Residents from a herdsman to a housewife share their views on what Obama has achieved and what they would like to see next. (Photo by Thomas Mukoya/Reuters)

Performers in costume perform in the rain during the parade on the second day of the Notting Hill Carnival in west London on August 31, 2015. Nearly one million people are expected by the organizers Sunday and Monday in the streets of west London's Notting Hill to celebrate Caribbean culture at a carnival considered the largest street demonstration in Europe. The Notting Hill Carnival started in the 1960s, when the area had a large population of immigrants recently arrived from the Caribbean and was notorious for its slums – a far cry from today when it is one of London's most expensive places to live. (Photo by Leon Neal/AFP Photo)

An African giant pouched rat sniffs for traces of landmine explosives at APOPO's training facility in Morogoro on June 17, 2016. APOPO trains the rats to detect both tuberculosis and landmines at its facility. Every year landmines kill or maim thousands of people worldwide. The trained rats sniff for explosive and so are able to detect the presence of landmines far faster than conventional methods which involve metal detection. (Photo by Carl De Souza/AFP Photo)

A Peru fan cheers of her team during a Quarterfinal match between Colombia and Peru at MetLife Stadium as part of Copa America Centenario US 2016 on June 17, 2016 in East Rutherford, New Jersey, US. (Photo by Chris Szagola/LatinContent/Getty Images)

Workers clean empty cooking oil containers at a roadside recycling workshop in Kolkata, India, July 13, 2016. (Photo by Rupak De Chowdhuri/Reuters)

A news reporter doing a stand up near a sea wall in Cedar Key, Fla., is covered by an unexpected wave as Hurricane Hermine nears the Florida coast, Thursday, September 1, 2016. Hurricane Hermine gained new strength Thursday evening and roared ever closer to Florida's Gulf Coast, where rough surf began smashing against docks and boathouses and people braced for the first direct hit on the state from a hurricane in over a decade. (Photo by John Raoux/AP Photo)

A woman in a USA sash, who would help show U.S. President Barack Obama to his seat, waits with other women in traditional dress for the start of the ASEAN Summit gala dinner in Vientiane, Laos September 7, 2016. (Photo by Jonathan Ernst/Reuters)

Behaviour: Mammals category. Giant Gathering by Tony Wu, USA. Dozens of sperm whales mingled noisily off Sri Lanka’s northeast coast, stacked as far down as Tony could see. This was a congregation of dozens of social units, like a gathering of the clans. Aggregations like this could be a critical part of the whales’ rich social lives but are rarely reported. Some two thirds of the population was wiped out before commercial whaling was banned in 1986. This kind of major gathering could be “a sign that populations are recovering”, says Tony. (Photo by Tony Wu/Wildlife Photographer of the Year 2017)