For example, when you move your hand back and forth quickly (or just any object), you see "two" in a way. When something quick is thrown, there's a line that is left behind that follows that object.
I suppose "afterimages" suits it the closest, but it doesn't seem to be the right term.
For the second example, I think "trail" works, but I don't think it works for the first example.
Is there any specific terms, or could it only be described?