Protestors affiliated with the Occupy Wall Street movement block the entrance to the Iowa Democratic Party headquarters during a protest on December 29, 2011 in Des Moines, Iowa. Thirteen people were arrested during the protest. (Photo by Andrew Burton/Getty Images)

Protesters clad in improvised protective gear prepare for a clash with police in central Kiev, Ukraine, Monday, January 20, 2014. After a night of vicious streets battles, anti-government protesters and police clashed anew Monday in the Ukrainian capital Kiev. (Photo by Evgeny Feldman/AP Photo)

A policewoman tries to stop an anti-Occupy protester from breaking a police cordon to charge at pro-democracy protesters during a confrontation in Hong Kong October 13, 2014. Hundreds of unidentified people, some wearing masks, tried to break down protest barriers in the heart of Hong Kong's business district on Monday, scuffling with protesters who have occupied the streets for the past two weeks. (Photo by Bobby Yip/Reuters)

An animal rights protester demonstrates for the abolition of bull runs and bullfights, three days before the start of the famous running of the bulls San Fermin festival in Pamplona, northern Spain, July 4, 2015. (Photo by Eloy Alonso/Reuters)

One of two 9-month old Cheetahs is seen after it was released into a quarantine facility at Zoo Miami on November 29, 2012 in Miami, Florida. The two sub-adult brothers who arrived today were captive-born on March 6th of this year at the Ann van Dyk Cheetah Centre just outside of Pretoria, South Africa. The Cheetahs, after being monitored and examined for a minimum of 30 days to insure that they are healthy and stable, will be featured in Zoo Miami's Wildlife Show at the newly constructed amphitheater and will continue the work of Zoo Miami's Cheetah Ambassador Program by making appearances off Zoo grounds at a variety of venues including schools and civic organizations. (Photo by Joe Raedle)

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)

Rio de Janeiro's state military policemen aim their guns during a violent protest in a favela next to Copacabana, Rio de Janeiro on April 22, 2014. Violent protests broke out in Rio's landmark beachfront district, Copacabana, following the death of a resident last weekend during clashes with the Army in a nearby favela. (Photo by Christophe Simon/AFP Photo)

Paint splattered police officers look on during clashes outside Top Shop on Oxford Street, during marches in protest at government cuts on March 26, 2011 in London, England. Thousands are taking part in the Trades Union Congress (TUC) organised march to Hyde Park where a rally will take place. Police say they are deploying 4500 officers. (Photo by Dan Kitwood/Getty Images)