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)

Children eat watermelons to meet the “beginning of autumn” at a kindergarten in Handan, China on August 7, 2015. Chinese tradition to eat watermelons or peaches before that day symbolises “biting away summer”. The solar term ‘beginning of autumn’ falls on 8 August this year. (Photo by Xinhua/REX Shutterstock)

Indonesian child jockey Egi, 8, poses for photographs as he participates in a traditional horse race marking Indonesia's 70th independence anniversary, in Bima, West Nusa Tenggara province, Indonesia, 08 August 2015. Horse racing is the traditional sport in the area and a cultural heritage which continues to be preserved by the people of Bima, a small city on the east side of Sumbawa island. Similar races also held in Sumbawa Besar regency and Dompu regency. (Photo by Mast Irham/EPA)

In this September 19, 2014 photo, explosives are detonate by Peruvian counternarcotics forces on a part of a clandestine grassy airstrip in the Apurimac, Ene and Mantaro River Valleys, or VRAEM, the world's No. 1 coca-growing region, in Ayacucho, Peru. The dynamiting of craters by Peruvian security forces into clandestine airstrips cuts into profits but hardly discourages cocaine traffickers who net tens of thousands of dollars with each flight flown from these airstrips. (Photo by Rodrigo Abd/AP Photo)

A restaurant in Chelsea is giving customers the ultimate post-pub treat – by selling a burger for £1,100. The world's most expensive burger, dubbed the “Glamburger”, is stuffed with a burger patty made from 220 grams of Kobe Wagyu beef minced with 60 grams of New Zealand venison and seasoned with smoked Himalayan salt. (Photo by Groupon)

A Palestinian protester, dressed as Santa Claus, reacts after inhaling tear gas fired by Israeli troops during clashes in the West Bank city of Bethlehem December 23, 2016. (Photo by Mussa Qawasma/Reuters)

A participant dances as approximately 70,000 people from all over the world gathered for the annual Burning Man arts and music festival in the Black Rock Desert of Nevada, U.S. on August 29, 2017. (Photo by Jim Urquhart/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)