This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Illusion edited. en The original image plus two stripes By joining the squares marked and with two vertical stripes of the same shade of gray it becomes apparent that both squares are the same mit edu Edward Adelson mit edu These checkershadow images may be reproduced and distributed freely CC Uploaded with Checker shadow