Pictures...Are they really removed?

I came across an article and i am not much amazed while reading it as i already have some hint about it.A new research has been carried out by cambridge university in which they had studied different social networking sites such as Facebook,MySpace and others,the main thing pointed out in the research is that when you delete your picture or pictures from social networking sites,infact they are not deleted and remains on the servers without your knowledge, unfortunately Facebook is also one of them.It was also pointed out that the webpage and photos resides on different servers, and whenever you delete a picture it only deletes it from webpage and pictures are not deleted from servers.But facebook claims that whenever a picture is deleted it is also removed from its servers. Dont knw what they want to do with alot of pictures?:P.Anyways dont upload the pictures that you dont want the world to see even after they are deleted..