Images of blood-smeared protesters have captured the drama of the unrest provoked by last month's election result and footage of the death of a young Iranian woman, Neda Agha-Soltan, has become an icon of opposition protests.
"The Tehran regime is scared of images. The authorities have launched a real hunt on visual reporters so that no professional photo or video of sensitive subjects will leave the country," the Paris-based organisation said in a statement.
Iran crushed the protests and in early July said most of the people arrested during the events had since been released.
Reporters Without Borders, an organization campaigning for press freedom, said five photographers were arrested less than a week ago.
It said the photographer Mehdi Zabouli was arrested on June 20, and his Franco-Iranian colleague Said Movahedi, on July 9.
Photographers Tohid Bighi, Majid Saidi, Satyar Emami, Marjan Abdolahian, and Koroush Javan were arrested on July 11, it said, and at least five others have been injured by police or militias.
Four days after the election, Iran banned foreign media journalists from filming or taking photos of the protests, or even leaving their offices to cover the events.