“Try nude models who worked in Fine Art Faculties in the early 1970s, hide all art books and smash naked archaeological statues,” read the statement, alluding to some recent protests staged here by ultra-conservative Islamists known as Salafis. “Then take off your clothes and look at yourselves in the mirror, then burn your body that you so despise to get rid of your sexual complexes forever, before subjecting me to your bigoted insults or denying my freedom of expression.”

Soon after the post went live, apparently admiring allies sent out Twitter messages in support, inaugurating the nationwide debate. “A feminist #Jan25 revolutionary posted her nude photo on the internet to express her freedom. I’m totally taken back by her bravery!!” one ally, Ahmad Awadalla, a human rights activist, said on Twitter.

Ms. Elmahdy did not respond to a Twitter request for comment, and her phone number was unavailable.

The uproar over her pictures echoes a debate that flared up in Tunisia last month on the eve of its first free election, when a television station broadcast a film that is critical of the Islamist takeover after the Iranian revolution. Although some liberals said they had hoped that the animated film, “Persepolis,” would warn Tunisians about the dangers of an Islamist victory in their country, one scene violated an Islamic prohibition against personalized depictions of God. The resulting outrage stirred protests across the country, and Islamists cited it as an example of the need to defend their faith as they rode to triumph at the polls.

But in Tunisia, it was not clear that many people had actually seen “Persepolis.”

In Egypt, on the other hand, since it appeared Sunday, the post with the naked pictures has been viewed more than 1.6 million times and has attracted more than 2,000 comments, though many are quite critical. “Freedom,” wrote one detractor, “is not the same as degradation and prostitution.”