https://travel.state.gov/content/travel/en/passports/how-app...
In the US, I had to take photos for driver’s license at least 4 times, for green card 1 time, and for passport 1 time, not in a single one of them I am smiling. Saw the DLs of my friends more than a few times (either at bars or clubs or while crossing the border or when the topic arrived naturally), and the breakdown of smiling vs not smiling is 40/60 at most (with a heavy lean towards not smiling)[0].
I partially agree though about the US being a bit special in the aspect of even just allowing people to smile in ID photos. In the previous country I lived in and where I had to take ID photos, it was explicitly prohibited to smile in those photos, and they would reject applications if someone did.
0. Purely anecdotal, as it could totally be the case that I just accidentally ended up befriending mostly those who don’t smile for ID photos.
However, the camera used at MVD is clearly more sophisticated than it appears, because if you install the Mobile ID app, your photo goes full "Harry Potter mode" and animates in a 3D rotation!
I don't recall any directions about my expression for the US Passport photo at the USPS station. However, they did attempt to reject the photo for strange technical reasons. I could not fathom the rejection because the photo had been entirely handled by the professional USPS clerk and I wasn't involved in generating it. I insisted on submitting exactly the same way a second time around and it was approved. It must've been a procedural glitch of some kind. Or the government knew I shouldn't be traveling to an ill-fated vacation, and was trying to gently dissuade me?