Concerned citizens of the French city of Marseille sternly rallied against a bill which would allow adoption by same-sex couples – but it’s this image, snapped by an AFP photographer, which is resonating with a huge and instant global audience.

Photographer Gérard Julien’s image of two young women kissing in front of the angry demonstrators has now been seen by hundreds of thousands of people sharing the photo on social networks around the world.

The rallies were taking place in 75 centres around France, organised by a group which also opposes abortion and marriage equality. A big pink banner read: “one father, one mother – we don’t lie to children.”

The two women in the photo told French gay magazine TÊTU that they’re both straight, but wanted to make an important point.

“I think we do not need to be gay to be supportive,” says kisser Julia. “It’s a gesture of solidarity, pure and simple. I am for what the protesters do not want.

“While we were kissing, [the protestors] were screaming, ‘You’re disgusting! You are not beautiful!’”

Taking the photo, Julien knew he’d captured an iconic moment. “I had an inkling that the picture – which touches on an issue that leaves few indifferent – would resonate across a large audience,” he wrote on his AFP blog. “But I confess that I had no idea just how much attention it would draw.

“Who knows, it could turn out to be the kind of image that only comes along once in a while in the career of a photographer.”