An afterimage is an image that continues to appear in the eyes after a period of exposure to the original image. An afterimage may be a normal phenomenon (physiological afterimage) or may be pathological (palinopsia). Illusory palinopsia may be a pathological exaggeration of physiological afterimages. Afterimages occur because photochemical activity in the retina continues even when the eyes are no longer experiencing the original stimulus.^[1]

The remainder of this article refers to physiological afterimages. A common physiological afterimage is the dim area that seems to float before one's eyes after briefly looking into a light source, such as a camera flash. Palinopsia is a common symptom of visual snow.

https://en.wikipedia.org/wiki/Afterimage

Definition of afterimage (m-w.com)

1: a usually visual sensation occurring after stimulation by its external cause has ceased

2: a lasting memory or mental image of somethingThe problem with the heros of myths is that, although they were once a reality or rooted in one, they rarely matched their lovely afterimage.— Irvin Faust