An undercover police officer, who had been marching with anti-police demonstrators, aims his gun at protesters after some in the crowd attacked him and his partner in Oakland, California December 10, 2014. Police said more than 100 demonstrators marched in Berkeley, California, which has a history of social activism. Under cloudy skies, turnout was smaller than earlier in the week, when demonstrators in the area threw rocks at police and shut down a major freeway. (Photo by Noah Berger/Reuters)

Father Christmas arriving at the Arding and Hobbs store in Clapham Junction, London, 2nd November 1926. (Photo by H. F. Davis/Topical Press Agency/Getty Images)

Afghan artists perform a re-enactment of the lynching of Farkhunda, a 27-year old woman, to protest against her killing in Kabul, April 27, 2015. Farkhunda, who was killed by an angry mob in front of police in the Afghan capital in March for allegedly burning a copy of Islam's holy book was wrongly accused, Afghanistan's top criminal investigator said on March 22. The killing has fuelled anger about the weak rule of law and corruption that is crippling the country's instutitions. (Photo by Omar Sobhani/Reuters)

A masked Burundian protester faces soldiers in front of a burning barricade during an anti-government demonstration against President Pierre Nkurunziza's bid for a third term in the capital Bujumbura, Burundi, 25 May 2015. Street protests continued on 25 May as the United Nations Secretary-General Ban Ki-moon condemned the killing of the leader of the oppsition party Union for Peace and Development (UPD) Zedi Feruzi who opposed Nkurunziza's bid. (Photo by Dai Kurokawa/EPA)

In this April 4, 2015, photo, Marilia Skraba, center, of Brazil, applies makeup while waiting to compete in the Miss Viva Las Vegas contest during the Viva Las Vegas Rockabilly Weekend in Las Vegas. The event draws thousands of people from around the world. (Photo by John Locher/AP Photo)

Award-winning photographer Alex Bernasconi has captured thousands of images – from hiding hippos to wandering zebras – in his travels across Africa. His amazing work features in a new edition of his book Wild Africa. These amazing pictures create a snapshot of the life of some of the planet’s most spectacular animals and natural habitats. Photo: “Wild Africa”. (Photo by Alex Bernasconi)

Members of a teenage girl gang convincing an unwilling recruit to join the gang, circa 1955. (Photo by Vecchio/Three Lions)

An adult chimp plays with a young chimp at Chimp Haven in Keithville, La., Monday, February 18, 2013. One hundred and eleven chimpanzees will be coming from a south Louisiana laboratory to Chimp Haven, the national sanctuary for chimpanzees retired from federal research. (AP Photo/Gerald Herbert)