People often have to wait in long lines to have their bags searched, their bodies patted down, their bodies scanned by an electronic imaging machine, their bags sniffed by dogs, and their identification cards examined. That's not the way we do things in America.
Photos of Naked Iraqi Prisoners Outrage Arabs - latimes
What it sees is the body itself, plus the dark outline of any jewelry or, presumably, any concealed weapon. Many of the sex slaves are Yazidis, a persecuted minority sect that the IS considers to be apostate "devil worshippers," in part because of the Yazidis' ancient connection to the region's pre-Islamic past.