I'm not sure where my mind's eye fits in... I'll do the online test posted earlier soon. I have a friend who has aphantasia, so I've 'tested' myself before to see what I think my mind's eye is like.
If you said to me, "Imagine an apple", a pretty detailed picture pops into my mind instantly. It flickers a bit, but I can generally 'hold' it, more or less, if I concentrate, and even zoom in or out, and rotate it to see it from different angles. The particular apple that popped into my head right now is a deep red one, with a little bit of yellowy striation near the top. It has a stem. It's sitting on a dark wood table. The 'focus' of the image in my mind is on the apple, so there's a background, but it's blurry. I can see the background has a fireplace, a wide, low, open one, with a fire blazing, and the bricks around the fireplace are very dark, blackish brown.
If I add the concept that this is a video image rather than a still image, now there is movement in the image, a play of light from the fire that bounces off the apple. There's also another light source in the image, from the left... it's probably a floor lamp that's 'out of the frame' I'm looking at, because it's not a strong light, more of a glow. I could rotate this scene in my mind if I wanted to, to see what kind of lamp it might be, and if you said 'add a chair to the scene', I could also do that. Something will automatically pop into my head, but I could change the chair if I don't like it and imagine one I like better.
This is an imaginary scene, as far as I know. I don't recognise the house, though I suspect that maybe I've seen an image like this some time in my life, and that's what my brain is generating from.
"Okay, now imagine a completely different apple, outside, on a tree". I can drop the current apple completely and now have an entirely different picture in my head. It's interesting, because the apple I'm now seeing on a tree does come from real life (though I didn't intend to do that) - it's one of the little hard, red-green apples that are only really good for cooking, and it's on a tree that really did exist in my childhood backyard.
Brains are SO interesting!