It was March 14, 1951, the day Albert Einstein turned 72. The famous physicist, who was born in Ulm, Germany, had already been living in the United States for many years. At the time, he was working at the Institute for Advanced Study in Princeton, New Jersey. A birthday celebration was held in his honor at the research center.  The paparazzi were lurking outside the venue when he left, hoping to hear one of the world-famous professor's witty quips about the global political situation — and to take the perfect birthday photo. Not a fan of media hype, and growing weary of being a spokesperson, Einsteinwas annoyed by their presence. Yet there he was, stuck in the back seat of a limousine, sandwiched between the institute's former director, Frank Aydelotte, and his wife, Marie, unable to escape the flashing bulbs. "Enough is enough..." he is said to have repeatedly shouted at the pushy reporters. "Hey, Professor, smile for a birthday photo, please," one shouts. In a gesture of annoyance, the unconventional free spirit stuck his tongue out at his pursuers — a moment that was captured by photographer Arthur Sasse. The picture quickly circulated around the world, becoming an iconic image.  The absent-minded professor with disheveled hair, who often forgot to put on socks, yet whose theory of relativity is still understood by only the world's most brilliant minds, was elevated to a mythical figure during the course of his own life. The cheeky snapshot also earned him pop icon status.  However, it was not the photographer who helped the photo achieve worldwide fame, but Einstein himself. He ordered numerous prints and cropped it so the Aydelotte couple could no longer be seen. He sent dozens of the photos to colleagues, friends and acquaintances. "The outstretched tongue reflects my political views," he wrote to his friend Johanna Fantova. In 2009, an original signed copy was sold for $74,324 (€62,677) at auction, making it the most expensive photo of the genius ever.  Einstein, who was Jewish, had fled Nazi Germany and knew what it felt like to be the subject of a government-led witch hunt. Thus, he did not condone the Cold War and the search for alleged communists instigated by Senator Joseph McCarthy, in which many politicians, intellectuals and artists were accused of being "un-American."  Einstein had a lot to say about such human stupidity: "The ruling of the dumb people can't be overcome because there are so many of them, and their voice counts as much as ours" reads an Einstein quote translated from German. "Two things are infinite: the universe and human stupidity. But I'm not quite sure about the universe yet," goes another of the professor's quips.   Einstein met this stupidity with genius — and a dash of humor.  Since it was taken on Einstein's birthday in 1951, the photo of him sticking out his tongue has been reproduced millions of times: on posters and t-shirts, greeting cards, mugs and murals. And even today, decades after his death, the revolutionary thinker and genius professor still has numerous fans, from young to old.  This article was translated from German by Sarah Hucal. 