I mean, not for demonstrating the fate of downvoters, but because it's related to the question.
- Does this contradict any rules in the site?
- If not, what criteria can justify it?
The optimal Stack Exchange question is like a dolphin - streamlined, quick, and
with a predilection for eating fish aesthetically pleasing. Basically, anything unnecessary should be removed. I've learned the hard way that the number of people who read the entirety of a post is inversely proportional to how long the post is1. Therefore, for your sake and theirs, the ideal thing to do is to write a question with all the necessary details, caveats, and constraints, and then edit down anything totally unnecessary. This may include unnecessary
It's said that a picture is worth a thousand words. In reality, it might be worth a thousand characters - at least, it may take up as much space as 1,000 characters. That's a lot of space, and can be distracting. My rule of thumb: Don't add an image to your post unless you really need it. 75% of the time, that rule alone can make the decision for you.
Let's say you really think that the image is necessary. As far as I know, there is no overarching Stack Exchange policy on violent images; there's certainly nothing in the content policy, although that does briefly mention sexual content. That said, as Grace Note has pointed out, (sexually) explicit material could lead to the network getting blocked, and the same logic could apply to violent images. Besides alienating outside users, you also risk offending Worldbuilding users who happen to be passing by. Remember, the youngest (legal) users are thirteen years old, and while that doesn't mean we have to keep everything PG-13, it's always best to consider that anyone could be dropping by.
Essentially, adding images like this will rarely make the question better, and will likely alienate people who might otherwise read and appreciate the question. In almost all cases, I'd recommend leaving it out. But if you really think the image is needed, consider using spoiler formatting:
. . . or simply just adding a formatted link to the image:
[Here's a related image (May be not safe for work)](Link to image)
1 Yes, my latest answer is over 13,000 characters long. So maybe there's a bit of hypocrisy here.