I'd say the third one is definitely NSFW and the first two are questionable. There's nothing overly graphic about the first or second but at the same time, does show a realistic dead body so it might make sense to ere on the side of caution. I'm open to other opinions here though.
I'd just take into careful consideration what NSFW stands for to make decisions like this.
Basically would I be comfortable looking at this when my boss or coworkers could walk in and see?
If the answer is no then there you go. Generally simple stuff.
Personally I'd flag all of these NSFW since it's relatively realistic depictions of dead bodies and/or lots of blood is shown. I'd prefer not to be grilled by Mr. CEO about why I'm looking at such violent images and threatening to get security involved when I should be turning in my quarterly report.
If the sheet is NSFW and the icon is basically a smaller version of the sheet, the icon probably isn't okay. In these cases, I'd zoom in and try to avoid showing any blood.
My guideline is usually this; if there’s blood and violence, SFW. If there’s blood and violence against a victim, NSFW.
If someone is swinging a bloody sword, SFW. If they’re stabbing someone through the chest, NSFW.
I'd say those are pretty good guidelines within reason though I'd still label the third icon shown here as NSFW because it has excessive blood/violence.
Is Mortal Kombat allowed?
Of course. That's comedic violence and I wouldn't even classify it as NSFW because of how exaggerated it is.
When it is utterly horrifying and you wanted to have some eye bleach after that. I wouldn't think these are NSFW.
If their bodies are naked, chopped, sliced..etc in a way that you don't like to look at it in a longer time, then it can be consider NSFW.
If you want a bloody-good example of a violent NSFW, look no further than Mai-chan's daily life.