How can anybody, including myself, be sure that what is seen is real?

How can anybody, including myself, be sure that what is seen is real?

How can anybody, including myself, be sure that what is seen is real? My right eye was scratched, and I can see this scratch-mark before "reality", as one would see their right hand before their left if they arranged the two that way. I wonder if this proves the external to be an actual place within something (the universe?), like it has an absolute position within my (a sentient being) perception. This brings me to my final question: How can I prove the distance between my two hands? When I look at my right hand in front of my left hand, I see them as two objects apart from each other, but I sometimes see a flat picture, like a movie screen: it is manifestly flat but produces 3-dimensional pictures. Does this mean that my eyes create reality to be other than what it is, like how they create depth to be where it really is not? Or does this mean that my eyes are perceiving reality as it should be perceived? Ugh! And the thought that those who cannot "see things" in ink-blots on white paper have learning disabilities peeves me. They should be proud that their minds do not create fallacies! That is what I think.

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