Actually I got the answer at Getty own forum, it is like this:

- If person seems recognizable, by any thing,  for example clothes or by other things, if it is believed that that person looking at photo can say - "it is me!" then it should have either model release or be editorial

To silhouettes - it must be totally  black, so if someone increase exposure or light and then see the details it is not acceptable. If silhouette is masked and filled by black color that there is no image left it could be accepted.