There is a good chance that the images will trigger a cognitive dissonance. The fence sitter may have to give up some deep rooted beliefs to accept that abortion is murder. Rather than giving up those beliefs, they will be mentally forced to strengthen their belief that abortion is not murder.
The nature of the deep rooted beliefs may include having had an abortion or having supported an abortion (husband, boyfriend, mother, father, sister, brother, friend, etc). For anyone of these people to accept that is abortion is murder, they will have to accept that they participated in a murder.
It may include having had a sibling aborted. In this case they would have to believe their parents are murders.
They may have friend who had an abortion. In this case they would have to accept that their friend is a murder.
They may have actively supported the Free Choice movement. In this case they would have to internalize that they actively supported murder.
The well known effect of cognitive dissonance is that the person does not remain as they were. Accepting the concept that would destroy the deep beliefs is so horrible that they must become more adament and vocal about the whole issue.
In other words, the images may very well convince a fence sitter that killing fetuses is all right.
This person is not a fence sitter, though it could be that they are someone who is beginning to seriously wonder if they've helped kill real human beings. In that case they will probably be looking for evidence to help them make up their mind.
I think the same is true in most of the other cases you have brought up.