As a person with aphantasia, I can see actual images when I'm on the edge of sleep, and I can see actual images when I'm dreaming, but I can't get anything like that to show up when I try to "picture" something. Just black with static.
It is difficult to describe, but so many people talk about it as if they are seeing something and I never have - I've always assumed it was a figure of speech of some kind to visualize something.