Singer Rihanna poses at amfAR's fifth annual Inspiration Gala in Los Angeles, California October 29, 2014. (Photo by Mario Anzuoni/Reuters)

New York Police Department tactical police officers stand guard near the New York Stock Exchange on September 9, 2011 in New York City. Officials are stepping up security in New York and Washington D.C. a day after U.S. officials received a credible but unconfirmed terror threat to utilize car bombs on bridges or tunnels in New York or Washington. (Photo by Justin Sullivan/Getty Images)

Park Ji-soo of South Korea performs her contemporary variation during the final of the 43rd Prix de Lausanne at the Beaulieu Theatre in Lausanne February 7, 2015. The Prix de Lausanne is an annual international dance competition for dancers aged 15 to 18. A total of 67 participants from 18 countries were selected from 300 applicants to take part in this year's week-long competition, from which the jury has shortlisted 20 finalists to compete for Saturday's finals. Six of this year's finalists will be awarded a one-year all expenses paid scholarship at one of the Prix de Lausanne's partner schools or companies, among the most prestigious in the world. (Photo by Denis Balibouse/Reuters)

A wounded member of the Afghan police reaction force waits for treatment in Alingar, Laghman province, on April 30, 2012. A bomb exploded next to opium poppy fields during a poppy eradication campaign in, wounding two Afghan policemen, police officials said. (AP Photo/Rahmat Gul)

A crew members walks on the flight deck past Super Etendard fighter jets aboard France's Charles de Gaulle aircraft carrier on missino in the Gulf, January 29, 2016. (Photo by Philippe Wojazer/Reuters)

A relic hunter dubbed “Indiana Bones” has lifted the lid on a macabre collection of 400-year-old jewel-encrusted skeletons unearthed in churches across Europe. Art historian Paul Koudounaris has hunted down and photographed dozens of gruesome skeletons in some of the world's most secretive religious establishments. Photo: Albertus in the church of St George in Burgrain, Germany. Incredibly, some of the skeletons, which took up to five years to decorate, were even found hidden away in lock-ups and containers. (Photo by Paul Koudounaris/BNPS)

French artist Olivier Grossetête used three enormous helium balloons to float a rope bridge over a lake in Tatton Park, a historic estate in north-west England.