system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are we not allowed to smile on our passport photos?
gpt
Some people look pretty different when they smile, enough so that they could be mistaken for someone else, or that someone else could more easily be mistaken for them.

So they get around this by having you make a neutral face, probably the same face you'd be making in line at the airport.  It speeds things up and prevents mistakes... Trust me, nobody's really judging you by your passport photo.