Innocent unless proven, right? I'm definitely not jumping in with those people traces of photos taken from other artists, but the "authorities" still have to have the proof that those really are photo traces. There are many artists out there that can draw perfect people silhouettes with an obsolete pencil, on top of that those (the thousand-pack thingy) could easily be traces of snapshots of low quality (actually a plan to do a snapshot photosession of silhouettes only in the future). The important thing is, I think, to add model releases even if the faces are obviously not recognizable.
p.s.: This is volatile territory, btw. With vector traces you can modify silhouettes ad infinitum. Scale the hip paths, flip a few arms, merge in a different hairstyle and noone will ever manage to lay charges on you.
p.p.s.: But you're right, morally the discussion goes beyond mere illustrations, traces or what-have-you.