Imagination is rea. Tots play pretend games and they believe in things like fairies exist. Unfortunately as children grow up they lose their imagination and they come a place where reality. Imagination is very important in everybody life.
Imagination is defined as the faculty or action of forming new ideas, or images or concepts of external objects not present to the senses. Not present to the senses meaning it cannot be heard, touched, seen, tasted or smelt. If something does not have any of these aspects then by default it is not real in reality, but metaphysically it is. Plus the things you see in your imagination do not happen physically (most of the time), or im sailing on a 60 foot solid gold yacht with two Swedish babes.
The Loch Ness monster is not technically part of imagination because people didn't imagine it, they thought they saw it. Because the Loch ness monster has been "seen" by the public it is now whats called an Urban Legend or Folklore. Imagination is part of our brain like dreams, which makes scenarios in our heads. Saying imagination is physically "rea" is like saying we can make anything happen instantly if we dream about it.
What your thinking of is iconic memory and that only lasts for 1/4 sec