I actually stumbled across that image a couple of years ago on a sports newsgroup. Among the angry denunciations in the reply posts that followed was a comment from someone who was familiar with the photo shoot. This individual claimed that the subject of the pictures was one of those people who has unusual control of her sphincter muscle, and was often seen in this type of pornography, which is created using colored water.
So what you are seeing is faked using dyes and an unusual talent. It isn't real. That may make people who have seen the image feel (somewhat) less nauseated.