As sex slave traders, the Islamic State in Iraq and Syria militant group appeared to have a system in place, including its own methodology of inventorying the women.
Women and girls were referred to as "Sabaya" (slaves) followed by their name. Some were bought by wholesalers, who photographed and gave them numbers, to advertise them to potential buyers.
Yazidi businessman Osman Hassan Ali, who has successfully smuggled out numerous Yazidi women, said he posed as a buyer in order to be sent the photographs. He shared a dozen images, each one showing a Yazidi woman sitting in a bare room on a couch, facing the camera. On the edge of the photograph, written in Arabic, was "Sabaya No. 1," "Sabaya No. 2," and so on.
Buildings where the women were collected and held sometimes included a viewing room. "When they put us in the building, they said we had arrived at the 'Sabaya market,'" said one 19-year-old victim, whose first initial is I.
"I understood we were now in a slave market," she said. She estimated there were at least 500 other unmarried women and girls in the multistorey building, with the youngest among them being 11.
When the buyers arrived, the girls were taken one by one into a separate room. "The emirs sat against the wall and called us by name. We had to sit in a chair facing them. You had to look at them, and before you went in, they took away our scarves and anything we could have used to cover ourselves," she said. "When it was my turn, they made me stand four times. They made me turn around."
The captives were also forced to answer intimate questions, including the exact date of their last menstrual cycle. They realised the fighters were trying to determine whether they were pregnant, in keeping with an injunction that a man cannot have intercourse with his slave if she is pregnant.
Recent escapees describe an intricate bureaucracy surrounding their captivity, with their status as a slave registered in a contract. When their owner sells them to another buyer, a new contract would be drafted. At the same time, slaves can also be set free, and fighters are promised a heavenly reward for doing so.
Though rare, this has created one avenue of escape for victims.
A 25-year-old victim who escaped last month, identified by her first initial, A, described how one day her Libyan master handed her a laminated piece of paper. He explained that he had finished his training as a suicide bomber and was planning to blow himself up, and was therefore setting her free.
Labelled a "Certificate of Emancipation", the document was signed by an ISIS judge. The Yazidi woman presented it at security checkpoints as she left Syria to return to Iraq.
ISIS recently made it clear that sex with Christian and Jewish women captured in battle is also permissible, according to a new 34-page manual issued this summer by its Research and Fatwa Department.
Child rape is explicitly condoned: "It is permissible to have intercourse with the female slave who hasn't reached puberty, if she is fit for intercourse," according to a translation of a pamphlet published on Twitter in December.
One 34-year-old Yazidi woman, who was bought by a Saudi fighter in the Syrian city of Shadadi, described how she fared better than the second slave in the household - a 12-year-old girl who was raped for days on end, despite heavy bleeding.
The fighter ignored the girl's agony and continued the ritual of praying before and after raping the child. "I said to him, 'She's just a little girl,'" the older woman said.
"And he said, 'No. She's not a little girl. She's a slave. And she knows exactly how to have sex. And having sex with her pleases God."
NEW YORK TIMES