So reading this has made me realise that my mental visualisation might not be normal. I definitely can't visualise images photo-realistically, there's maybe a similarity to synesthesia where I visualise some colours but I know it's my mother, a room, etc and it's sort of helpful for remembering other properties of that thing I'm visualising. Some things I can kind of visualise photo-realistically (in the sense it might be similar to a dark room where you only catch flashes of the thing): things I build from first principles (like say a mental model of a pulley system or an electronic circuit).

I'd literally always assumed this was just how peoples brains worked, I'd be interested in hearing if this is or isn't similar to other people.