you see it with your mind. How do you do that?
Sry, this whole time i've been saying nonsense let me change what i ment.
No one actually sees what they imagine. Instead they receive images differently than their eyes do. and it's usually at the corner of their eyes or when their vision is blurry. While what they see can be nothing more than a book shelf or a computer in the corner of their eye, they can perceive it as an animal, person or even a ghost. Meanwhile they still do not see anything differently they only "think" they did.
As for imagination, you never see it. You think about it. You imagination are you're dreams and such. How you see your dreams I simply do not know. You're eyes don't see. They just moderate the amount of light being reflected into your skull. You're mind takes that reflected light and forms images out of it. It even changes the light received since it also needs to change the image right side up since the eyes take it in upside down. While this process is happening I suppose there can be some sort of error cause this "data" to be distributed wrong allow your thoughts to be mentally projected into this image. Who knows? I don't.