Here you can see the varying degrees of strictness in Islamic dress in Tehran. The woman on the left is wearing the strictest form of Islamic dress. As you can see, her hair doesn't show and her black robe covers her entire body, almost to her feet. It's not uncommon for women to go beyond this and cover all but their eyes in the Arab world. On the other hand, the two women who are right and center are wearing a looser Islamic dress showing their hair and their robes end at about the thigh.
Photo by Hessam Parzivand