Some employees of the popular social-networking site Facebook have the full-time job of scanning the images posted to user pages and deleting those that are explicitly sexual or contain images of underage drinking or illicit drug use, Newsweek reports in its May 18 issue.

Facebook officials have developed detailed criteria on what can and cannot be depicted on user pages as the company seeks to make the site as advertiser-friendly as possible. On the sex side, there are semiformal guidelines like the "Fully Exposed Butt Rule" and the "Nipple Rule," while company policy also prohibits photos such as a girl blowing a cloud of marijuana smoke or an underage youth holding liquor bottles.

Some prohibited content is found with software-aided searches, but users also can flag pictures or other material they object to for investigation.

"If [Facebook] got polluted as just a place for wild and crazy kids, that would destroy the ability to achieve the ultimate vision, which is to create a service for literally everyone," said David Kirkpatrick, author of the soon-to-be-published book "The Facebook Effect."

About 150 of Facebook's 850 employees help police the site. In addition to deleting objectionable content, they also fight spammers and work with law-enforcement agencies to investigate crimes where victims' or perpetrators' sites can provide valuable clues and information.

Unlike some other social-networking sites, Facebook requires users to sign up using their real names, making policing easier.