Image: Grey square optical illusion

Description: An optical illusion. Square A is exactly the same shade of grey as square B. See demonstration.
Title: Grey square optical illusion
Credit: File created by Adrian Pingstone, based on the original created by Edward H. Adelson
Author: Original by Edward H. Adelson, this file by Gustavb
Permission: The copyright holder of this work allows anyone to use it for any purpose including unrestricted redistribution, commercial use, and modification. Please check the source to verify that this is correct. In particular, note that publication on the Internet, like publication by any other means, does not in itself imply permission to redistribute. Files without valid permission should be tagged with {{subst:npd}}. Usage notes: • If the work requires attribution, use instead • If this is your own work, please use Template:Cc-zero instead Copyrighted free use //commons.wikimedia.org/wiki/File:Grey_square_optical_illusion.PNG
Usage Terms: Copyrighted free use
License: Copyrighted free use
License Link: //commons.wikimedia.org/wiki/File:Grey_square_optical_illusion.PNG