It is one of the iconic photographs of the 20th Century, an image that is synonymous with love and with Paris, the city of romance. Its name is Le Baiser de l’Hôtel de Ville (The Kiss by the Hôtel de Ville) and an exhibition at the Martin-Gropius-Bau in Berlin is currently displaying it alongside another hundred or so pictures by the great French photographer Robert Doisneau.

“People like my photos because they see in them what they would see if they stopped rushing about and took the time to enjoy the city,” Robert Doisneau used to say. It is very true, however, perhaps surprisingly, his most famous picture was staged, says Francine Deroudille, Robert Doisneau’s daughter and co-curator of the exhibition, as she reveals the story behind Le Baiser de l’Hôtel de Ville to BBC Culture.

“The picture was taken in the spring 1950. My father’s agent had pitched a series on ‘the lovers of Paris’ to American publications and Life magazine had commissioned it,” Deroudille explains.

Truth here lies in the beauty of the impulse and a spontaneity that is closely linked to the French spirit and its capital city

At the time, image rights were already protected by law and a cautious Robert Doisneau preferred to use friends or young actors to feature in some of his commissioned reportage, in order to avoid legal issues. One afternoon in March 1950, Doisneau went out into the streets of Paris with young actor friends and just let them be: they walked, held hands, talked, and kissed, with Doisneau never far behind. “His models weren’t models in the sense that they didn’t pose. Doisneau was simply catching them flirting and kissing, in a very natural way, ” says Deroudille.

The result, a kiss caught at the corner of rue du Renard and rue de Rivoli right across from the city’s town hall, feels like the best of Doisneau: a suspended moment whose beauty is known only to the lovers and the photographer. Around them, indifferent Parisians walk, hardly noticing the young couple; cars shoot by and people seated at a café (now a shoe shop) speak animatedly.

But, we, sharing Doisneau’s gaze, stop in our tracks in front of this picture: the immediacy of it, the young bodies’ movement and the place and time, Paris, 1950, cast a spell on the viewer. Who cares about authenticity? The sentiments showed in the picture are authentic. Truth here lies in the beauty of the impulse and a spontaneity that is closely linked to the French spirit and its capital city.

“At the time, American magazines were very keen on Paris stories, especially stories covering the life in Paris streets where people behaved much more freely than anywhere in America. Even in New York’s streets, couples weren’t seen kissing, and certainly never with such carefree abandon,” says Francine Deroudille.

However, after it was shot, and published in Life Magazine, the picture remained just one of many in the very large Doisneau portfolio (today totalling 450,000 negatives, and managed by his two daughters Francine and Annette). Doisneau himself didn’t think it such an extraordinary picture.

“He thought it was well composed but nothing more” says his daughter. “And then, 30 years later, in the early 1980s, a young publisher suggested to publish it again, in poster format. Doisneau wasn’t convinced but all the young people at the Rapho agency where he worked were so enthusiastic that he accepted.” The success was instant and global. How did Doisneau explain his picture’s sudden and universal success? “We all realised that it represented a perfect fantasy. It encapsulates the world’s view of Paris as the city of love and freedom.”

‘A humanist photographer’

Robert Doisneau’s photographs are intimately associated with Paris at a time when the city was the world capital of arts and culture. “He was in awe of Paris and his love never faltered until his death in 1994,” says Deroudille. Doisneau documented Paris’s evolution from the 1930s up to the late 1980s; he saw and often welcomed both social and architectural changes. “Paris has this intrinsic beauty which touches everyone who visits or lives here. Paris has this ability of making you happy, it certainly made him very happy,” reveals Deroudille.

Doisneau wasn’t the only one fascinated by Paris’s grandeur and its myriad small pleasures. Eugène Atget, Henri Cartier-Bresson, Brassaï, André Kertész, Willy Ronis, Robert Capa, among many others, have made Paris the most photographed city of the 20th Century. Their pictures have shaped the world’s perception of the city, enhancing and enchanting the reality. Decades later, we still see Paris as a place where mystery and charm take you by surprise at almost every corner.

Paris streets, in which Parisians lived day and night to escape small, shabby and decrepit lodgings, offered the best of theatre

Much of Doisneau’s work came out of commissions from newspapers and magazines, but he always used his assignments as opportunities to catch moments that interested him personally. With his Rolleiflex, he photographed building facades, interiors, river banks, children playing, passers-by, wedding couples.

“He felt comfortable everywhere, in the poor areas and the posh districts of Paris. What he enjoyed most was to show all the facets of Paris even if he had a particular fondness for Paris’s children and its working class,” says Deroudille. Often referred to as a ‘humanist photographer’, Doisneau’s pictures focused on people by making the private and the personal visible. For decades, Paris streets, in which Parisians lived day and night to escape small, shabby and decrepit lodgings, offered the best of theatre. “Parisians don’t live as much in the streets as they used to, however, cafés’ terraces, the habit of walking and ‘flâner’, the concentration of shops such as bakeries and food markets, mean that the spirit remains and continues to fascinate visitors,” says Francine Deroudille.

But what would Doisneau make of today’s photography? Of selfies and Instagram fads? “He would have loved to see that photography had become accessible to all. However, [I] am sure he would have been aghast by the selfie culture which, in many ways, is a vain obsession with the self to the detriment of a wider view,” says Deroudille.

Doisneau, a modest man, valued empathy with others, simplicity, and above all, spontaneity.

If you would like to comment on this story or anything else you have seen on BBC Culture, head over to our Facebook page or message us on Twitter.

And if you liked this story, sign up for the weekly bbc.com features newsletter, called “If You Only Read 6 Things This Week”. A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday.