Entoptic

Under suitable conditions light falling on the eye may render visible certain objects within the eye itself. These perceptions are called entoptical.

Entoptic images differ from optical illusions because, whereas illusion is a phenomenon happening in the brain, entoptic phenomena take place within the observer's own eye. In this sense, the observer cannot share this experience with others, because in fact the image is caged within his eyes.

What does it mean to own an image?
And a non-image?