When Masih Alinejad, 37, posted a picture of herself online jumping in the air in a sunny, tree-lined London street, the journalist was hoping to cheer up readers weary of her stories of grim human rights cases in her native Iran.

She did not expect what followed: a Facebook phenomenon that gained half a million followers in a month and scathing, personal criticism by Iranian state television, which accused her of drug addiction, perversion and insanity.

Inspired by Alinejad's photo, taken in a public place with her head uncovered by the veil that is obligatory in Iran, thousands of women in Iran uploaded similar images. The page is called "My Stealthy Freedom."