Two guards perform an execution in China, one holding the gun, the other holding a mask over the victim's face. (Photo by General Photographic Agency/Getty Images). Circa 1925

Yuri Gagarin does not always show up in full-scale astronautics. In this picture he smiles during his summer vacation in Sochi, Russia in 1961 with sunglasses and sunhat in the camera. (Photo by Imago/Eastnews)

Peter Stringfellow, 1994. He was an English businessman and nightclub owner. Stringfellow started in the nighttime trade in the early 1960s and recalled booking acts including The Beatles, The Kinks and Jimi Hendrix to play at his clubs. Peter Stringfellow has died aged 77 on June 7, 2018. (Photo by Rex Features/Shutterstock)

Prince Philip, Duke of Edinburgh practicing his bicycle polo technique, Windsor Great Park, Berkshire, 1964. (Photo by Norman Potter/Daily Express/Hulton Archive/Getty Images)

Pablo Picasso, famed 66-year-old Spanish artist who has lived most of his life in France, suns himself on a boat on the beach at Golfe Juan in Vallauris on the French Riviera on March 10, 1948. Entering a new period in his varied artistic career, Picasso has turned to painting pottery at the nearby town of Vallauris. (Photo by AP Photo)

Children play on top of an old plane's fuselage at a dump site in Paranaque city, Metro Manila, Philippines January 21, 2017. (Photo by Ezra Acayan/Reuters)

Dutch collaborators under arrest at Nijmegan, Holland. They were rounded up after the capture of Nijmegan Bridge by the Allies. (Photo by H. Warhurst/PNA Rota/Getty Images). 1945

Brain-on-a-chip. Dazzling in green and magenta this image shows the nerve fibres (in green) produced by neural stem cells (in magenta) as they grow on a synthetic gel. Captured by a technique known as confocal microscopy, the image is part of research shedding light on how tinkering with the environment can affect the way in which nerve fibres grow. (Photo by Collin Edington and Iris Lee/Massachusetts Institute of Technology/Wellcome Images)