Hundreds of Iranian women have posted photos of themselves without the hijab in a Facebook group called "Stealthy Freedoms".
The page was set up 10 days ago and has already attracted over 143,000 likes as men and women alike rush to upload veil-free pictures, in a subversion of the country's strict Islamic codes - and in a bid to kick off a wider debate about personal freedom.
Wearing the hijab has been compulsory for women in Iran since the 1979 revolution and the establishment of an Islamic state. Not wearing one can be punished by anything from fines to jail time, with the country's morality police patrolling streets to see that the rules are upheld.
The veil-free Facebook group was set up by London-based Iranian journalist Masih Alinejad, who told the BBC: "My hair was like a hostage to the government.
"The government still has a lot of hostages."
Facebook is officially banned in Iran but around four million people are believed to use the site on a regular basis and the Stealthy Freedoms page has attracted around 20,000 members per day since it was launched over a week ago.
The photos show women joyously posing without their veils on the beach, in parks and against the backdrop of cities such as Tehran.
The pictures are accompanied by a host of likes and comments.
"Freedom is sweet even for one second," writes one contributor, as another - who posted a photo of herself in a field of flowers, commented, "Feeling the wind blow through my hair was a strange feeling, I wish we could always experience it."
One woman who sent a picture of herself in the woods wrote: "I took this picture stealthily in the spring. It makes me feel happy."
Another woman who uploaded a picture of herself beside Iran's picturesque Valasht Lake said: "Oh, the dancing of wind through my hair! Even for a few moments. I was bursting with happiness to feel the wind through my hair without someone around to see it and warn me to keep covered properly."
One grandmother who joined the campaign with a photo alongside her mother and daughter wrote, "We wish that the new generation tastes this most basic freedom before their hair goes gray. Is this too much to ask?"
The Facebook site's founder Alinejad told the Guardian she had barely slept since starting the group last week, because she had been inundated with messages, photos and stories from women inside Iran.
The journalist is best known for her hard-line interviews with Iranian officials and her work to expose human rights violations.
She grew up in an Iranian village in the north of the country and wore a hijab every day until she left for London in 2009.
Alinejad says she's not opposed to the veil - her mother wears one - but she supports the right of Iranian women to choose either way.
"I have no intention whatsoever to encourage people to defy the forced hijab or stand up against it," she said. "I just want to give voice to thousands and thousands of Iranian women who think they have no platform to have their say.
"Iranian women may not have a lot of freedom but they have always known how to go around the system and find it," she added to the Wall Street Journal.
"Social media has turned into a mirror for Iranian women to be able to reflect the realities of their lives."
As summer gets underway in Iran and the mercury approaches 40C, many women start bending the rules with looser hijabs, a hint of hair, or the odd glimpse of a bare ankle or painted toenails.
"These little stealth freedoms might seem so trivial, but they are vital to your soul. And I’ll carry these tiny freedoms with me in each step I take till I reach absolute freedom at last," writes one woman on the Facebook page.
Police can and will issue fines or detain people for such "un-Islamic" behaviour, but it's becoming more and more difficult to enforce.
The hijab is a controversial issue in Iran. Iran's new president Hassan Rouhani last year signalled a softer approach to Islamic dress code and web censorship.
"The freedom and rights of people have been ignored but those of the rulers have been emphasised…, Rouhani said, in a post-election interview. "Restricting [people's right] to criticise will only stifle and lead to inefficiency.
"If a women or a man does not comply with our rules for clothing, his or her virtue should not come under question… In my view, many women in our society who do not respect our hijab laws are virtuous. Our emphasis should be on the virtue."
However, other conservative political forces such as Iran's Revolutionary Guards still wield a lot of power and are calling for stricter enforcement of dress codes, in accordance with the country's Islamic laws.
Fars News Agency, a semi-official news outlet affiliated with the Revolutionary Guards, has denounced the Facebook page and accused Alinjead of working with Iran’s enemies to promote promiscuous behaviour.
What kind of difference the campaign will make to the political agenda remains to be seen, but it is an important platform for a debate about personal freedom and social expression.
As one woman writes, "Hoping for the day when all my nation’s women can taste freedom with their whole bodies and souls."
Photos: Facebook, Words: Anna Brech