Is it leaning to one side?
The truth is that each square that makes this image up is the exact same size. Some have white borders and some have black borders but the whole image is plumb. That is to say that the lines vertical and horizontal are all respectively parallel to each other.
To paraphrase a nursery rhyme despite the title above this is not the "The Crooked Man's Optical Illusion"
Herman J. Verwaal
Herman has a large collection of optical illusions that he has created over time. He has generously allowed me to feature a few of his pieces here. This is just one (check the sitemap for his others) of many. His illusions run the gambit and I will be showing you more of his excellent Trick-Art in the future.
Thank You for sharing these excellent illusions Herman.