Scores of men have responded to the hijab campaign
Iranian opposition supporters have launched an online campaign to free a student activist accused of dressing as a woman to try to avoid arrest.
Hundreds of men have posted photos of themselves wearing Islamic headscarves as part of the "Be a man" campaign to show solidarity with Majid Tavakoli.
He was arrested during protests in Tehran on Monday and state media showed images of him in headscarf and robes.
The opposition say the pictures were staged in a bid to discredit him.
They say he was not wearing the headscarf and robes when he was arrested.
Iranian state media say Mr Tavakoli was arrested as he sought to leave Tehran's Amir Kabir university "disguised as a woman" after Student Day protests.
He is a leading activist who spent 15 months in jail along with two fellow students after being arrested in 2006 on charges of insulting religion and the country's leadership in student publications, AFP news agency reports.
One US-based website for Iranian expatriates, iranian.com, has posted scores of photos submitted by readers.
"Iranian men are showing their solidarity with Tavakoli by wearing a hijab and posting their photo on the web," reads its appeal to send in photos.
Some of the website's readers argue that the campaign is also a gesture of solidarity with Iranian women, who are obliged by the authorities to wear the hijab in public.
Many of the contributors openly show their faces, in headscarves, while some have all but their eyes covered.
"Life is so short and so many fine, fine men around," one woman reader quipped.
"It is getting harder to be a girl these days."