Spacewalker Mark Vande Hei took his own photograph during the first spacewalk of 2018, on January 23, 2018. These sky-high pictures are better known as “space-selfies”. (Photo by Mark Vande Hei/NASA)

Rohingya refugee sisters Nur Kaida (R) and Ruhana hug each other at their shelter at the Palongkhali refugee camp near Cox's Bazar, Bangladesh December 21, 2017. (Photo by Marko Djurica/Reuters)

Cropped shot of a woman flirtatiously touching leg of man in a suit with her foot under the table. (Photo by LightField Studios/Skyfish Digital Media/Getty Images)

A Southwest Airlines jet takes off from Reagan National Airport with a thunderhead to the east on June 20, 2017 in Alexandria, VA. (Photo by Jonathan Newton/The Washington Post)

The sky looked on fire this morning, as it made the clouds glow red, just before sunrise at Peterborough Rowing Lake, in Nene Park, UK on January 18, 2017. (Photo by Paul Marriott/Rex Features/Shutterstock)

Bikini Contest in Daytona Beach, Florida, USA. (Photo by Evan Hurd/Sygma/Sygma via Getty Images)

Racegoers in fashionable hats attend Ladies Day at Cheltenham Festival on March 15, 2017 in Cheltenham, England. (Photo by David Davies/PA Wire)

A girl collects water lily flowers at a pond in Kampong Speu province Cambodia, March 24, 2017. Picture taken March 24, 2017. (Photo by Samrang Pring/Reuters)