The photograph was published in several leading newspapers including Okaz, Ashahrq al-Awsat and Al-Watan, each with a close link to senior members of the ruling royal family.
No reason was given for why the picture was published only now; accompanying text gave a routine description of the theme of the conference.
But the photo appeared amid a mounting and increasingly open debate over the country's harsh ban on unrelated women and men mixing together enforced by ultra-conservative Saudi Muslim clerics.
In the past 10 days the outspoken head of the Mecca branch of the Saudi religious police, who enforce official Islamic morality, was fired and then mysteriously reinstated after he broke ranks to say that there was nothing in Islamic tradition and law banning mixing.
Newspapers reported vaguely that a high-level figure had intervened to save Sheikh Ahmed al-Ghamdi, after the president of the Commission for the Promotion of Virtue and Prevention of Vice, or religious police, signed and published an order naming his replacement.
Most of the women in the photograph on Friday were also baring their faces, against leading clerics' insistence, often enforced by the religious police, that women's faces must be covered in public.
King Abdullah has not publicly spoken out on the debate. But last year he opened a new science university named after himself that permits the international body of students and faculty to freely mix together.
When a senior cleric criticised the university, he was summarily fired by order of the king himself.
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