Congruent Image

The said picture is presented on this page. As said it is an example of symmetric congruent image. But how can you say that the image above is congruent to the image below? We can say that the two images are the same but are they congruent? What is the difference between similarity and congruence? Do they have the same idea in some?

I would like to ask you to write your thoughts about what I've written and on this picture on the comment section below. 

This photo was taken from google. (https://www.alamy.com/stock-photo-abstract-image-of-two-modern-urban-worlds-located-upside-down-to-each-170466013.html)