As someone who has actively written algorithms for passport security verifications, including photo strict requirements and validation, this post really struck a chord with me.
I expected the layout, head size, expression etc rules to be more or less standard across countries. More than a decade a go our dual citizen baby got both passports at once and I thought I could use one of the US duplicates for the other country... an hour of fiddly standards checking, measuring, reprinting, cropping and I got something that would pass on the application but got a scolding that it was not quite right.