I have some very loud voices in my head. One is intentional, like when I read or write things out I hear my own voice in my head. At least one of them just talks shit to me all the time. It's not like schizophrenia "I hear voices", it's just a thought that I'm not actively having. When my depression gets bad it's gets really loud so I drown it out with music and books.
I can't see pictures in my head.
On another note, I'm pretty sure religious nutjobs really hear their own inner monologue and think it's a god talking to them. That's why their god always agrees with them.