Thomas, yes, talking about Escher can only be nice.
In my comment I used the word - almost.
I believe that Escher can be used in photographic terms.
The image that Jacques posted had the same grey tones as Escher's graphics. Also, it makes trick on you as to what you saw in the image. Escher was bending both ways and probably in ways that we cannot even comprehend. His museum is here in The Hague and I often visit and admire his metamorphosis works
Just like in Hofstadter's Pulitzer winning masterpiece - Godel, Escher, Bach, I believe that art and science are interconnected.
Hence, photography is both art and science