There are no hard and fast guidelines. It's a matter of ethics and a call by editors. usually when things like this happen, there is some discussion- but also usually the photo isn' submitted! example: I once took some shots at a car accident; a man had driven his motorcycle into the back of a piece of farm machinery. a spike on the machine had gone through his head, which was still stuck on it when I arrived on the scene. the rest of his body and the bike were a couple of meters away on the pavement. i took the shots, but the photo they published? tight close up of his hand gripping the handle of the bike, and a regular portrait shot of him when he was alive.

WHY? because my editor deemed, after discussion with me and several others in the newsroom, that there was no news value in publishing a photo of a disembodied head.

the problem of course, and as I keep saying, is BECAUSE there are no hard rules on what you can show or say, you need quality people doing the work. and if you skimp on quality people, this is what happens. I can guarentee before the staff shakeups this wouldn't have happened, and if it did? they would have been prepared with reasons to defend it.