Can you smile in a passport photo?
No. It is one of the few rules that is the same everywhere we have checked, and it is worth understanding why, because knowing the reason tells you where the line falls.
What the authorities say
Canada is the most explicit: a neutral expression means eyes open and clearly visible, looking straight at the camera, mouth closed, not smiling and not frowning. The ICAO standard behind most of the world's passports says the same in more formal language, and the UK and US requirements follow it.
Why the rule exists
Not because a passport is meant to look grim. Facial recognition measures distances between fixed points, and a smile moves several of them at once: it raises the cheeks, narrows the eyes and changes the width of the mouth. A neutral face is the reproducible one, which is what a border gate is trying to match against.
Where the line falls
Closed lips with a very slight upturn usually passes. Teeth showing does not. Neither does a mouth slightly open, which is the version people fall into without noticing when they are told to relax. The failure mode worth knowing is that you cannot see it in your own photo, because it looks like your ordinary face to you.
The exception, and it is narrow
Small children are treated differently in several countries, on the sensible grounds that an infant does not take instruction. Beyond that, the exceptions are medical rather than personal preference, and they generally require documentation rather than an explanation at the counter.
Questions
Can you smile in a passport photo?
No. Every authority we track requires a neutral expression with the mouth closed. Canada spells it out as not smiling and not frowning.
What if I have a naturally upturned mouth?
Closed lips are what matters. A face that rests slightly upturned is not a smile, and it passes as long as your mouth is closed and your expression is not exaggerated.
Why is smiling banned when it is just a photo?
Because the photo is measured, not looked at. A smile shifts the cheeks, eyes and mouth at once, which is exactly what facial recognition uses to match you at a border.
Do the rules apply to babies?
Several countries relax the expression requirement for very young children, because an infant cannot follow the instruction. Check the specific application, because the age threshold differs.