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Due to the PNG signature ("magic bytes"), every PNG file starts with the sequence "89 50 4E 47 0D 0A 1A 0A".

In ASCII: "[\x89]PNG\r\n[SUB]\n"

Is there any information on the origin of these bytes? Why were they chosen like that?

So you'd get "PNG" printed out when you accidentally "type"ed that file in MS-DOS. The 1A was the EOF character for text data back then.

Ah, that makes a lot of sense!

So what's 0x89 at the start? It's outside the ASCII range.

So when a 7-bit transfer masks out all highest bits, it becomes a invalid signature instead of the pixel data getting silently corrupted.