It's a good illusion, but isn't this just a variant of the dots used in old colour comic books and some op art prints? For example, <a href="http://facweb.cs.depaul.edu/sgrais/images/Color%20Comics/Kid.jpg" rel="nofollow">http://facweb.cs.depaul.edu/sgrais/images/Color%20Comics/Kid...</a> and <a href="https://legionofandy.files.wordpress.com/2016/04/big-tarzan.jpg" rel="nofollow">https://legionofandy.files.wordpress.com/2016/04/big-tarzan....</a>