There's a certain amount of controversy brewing within the social networking scene, with Facebook disallowing any images of women breastfeeding to be posted on the site in case nipples are exposed - however, they appear to adopt a much more slack approach in allowing "graphic images" of animals portrayed "in the context of food processing or hunting as it occurs in nature". Similarly, images of bodily fluid (except semen) can be posted as long as no human is featured, yet "deep flesh wounds" and also "crushed heads or limbs" are acceptable as well as images of people using marijuana but should an image feature "drunk or unconscious" people, then it's a completely different story.
Apparently this is Facebook's approval system for images and posts, exposed by a leaked document from oDesk, an outsourcing company. The leaked file is a 13 page manual that receives constant updating, to be followed word for world by all oDesk employees - with oDesk in charge of the regulators monitoring the aforementioned posts and images which they receive when a Facebook users clicks on the "Report" button.
Regarding the appointment of a third party to undertake this job, a spokesman for Facebook explained in the Guardian: "In an effort to quickly and efficiently process the millions of reports we receive every day, we have found it helpful to contract third parties to provide precursory classification of a small proportion of reported content."