As a general rule of thumb, images should be used when they provide a significant advantage over text for the post.
I'm not seeing that in this case. Both images could easily be collapsed into a single phrase "…punish themselves, often to the point of drawing blood." with no loss of relevant information.
As I see it, the only "advantage" to using images in this case is for shock value, to show how "bad" such actions really are. This is a tactic often used by polemic sites and forum arguments, and as such I feel that it really has no place on here; it makes us look unprofessional and is more likely to drive away actual experts and instigate sectarian squabbling than it is to achieve anything useful.
As for what should be done when the author is adamant on keeping a (potentially) problematic image? Flag the post for moderator attention (we can lock such posts to prevent edit wars) and bring it up to meta for discussion. Once a reasonable resolution is reached in meta, flag a moderator to unlock the post (if the lock hasn't degraded naturally) so the post can be edited accordingly.