Maybe the rules vary in different countries and certainly there is enough confusion about the whole matter.. And I had always thought that the rules were that if taken in a public place it was legitimate to post an image permission given or not, regardless if it was an identifiable person or Joe Public..

Taking shots of a model is another matter, and in particular when there may appear to be any suggestion of underage, And nude images are far more liable to need them,  and Stock image libraries are not very keen to accept work from anything other than professionals, to limit the amount of work that they would have to do in chasing up properly completed model release forms..  Certainly the staff would question this with any image, and many have had to be withdrawn if a proper model release was not forthcoming..  This is also true I am sure here on Rendo as well.

The onus for taking responsibility for model releases is more the responsibility of the photographer and the organisers if an event of some sort that is not  open to the public at large.   

Danny O'Byrne  http://www.digitalartzone.co.uk/

"All the technique in the world doesn't compensate for the inability to notice" Eliott Erwitt