The brain does not really have difficulty with camera angles. Almost every single optical illusion / visual trick / visual quirk is actually an example of how i

The brain does not really have difficulty with camera angles. Almost every single optical illusion / visual trick / visual quirk is actually an example of how incredibly clever and well-optimized the brain is. The fact is the brain takes convenient shortcuts whenever possible. The ability to detect smiles is indeed conducive to social behavior in humans. But the ability to distinguish smiles on upside down faces is not particularly useful for anything in real life. It's just an interesting quirk. The brain just recognizes the smile, and shortcuts any additional (useless) post-attentive processing.