>There are quite a few optical illusions photos based on that, for example the face that seems to smile - until you flip it.

Ah, the Thatcher effect! [0][1] Although IMO this is a bad example because (er, AFAIK) we don't have the same sort of hardcoded facial-feature-recognizer systems in computer-vision neural nets as we do in boring old hew-mons. The Thatcher effect works on people with prosopagnosia [2] ('face blindness', people who have to work out who you are by your clothing, gait, voice and body language). These, taken together, proved that the known full-face-detector in humans, the fusiform gyrus, is aided by other systems that recognize features of a face (eyes, mouth) independently of that face's vertical orientation.

[0] https://en.wikipedia.org/wiki/Thatcher_effect

[1] http://static.independent.co.uk/s3fs-public/styles/story_med... < here's the trope-namer, straight outta the 80s. The effect is much more pronounced in this image than in the wiki one; it's way more obvious that the mouth/eyes are 'properly oriented' despite being upside down

[2] https://en.wikipedia.org/wiki/Prosopagnosia