A neutral expression photo shows a relaxed face with the mouth closed and no exaggerated emotion — not a frown, but not a full smile either. Passport, visa, and many ID photo rules require it specifically because a strong expression can distort facial features enough to interfere with automated face-matching.
Why identity documents require it
Face-matching systems compare geometry — the distance between eyes, the shape of the jaw, the position of the mouth. A wide smile or a raised brow shifts all of that measurably, which is why passport and visa rules ask for a neutral expression specifically rather than "look natural." It is a technical requirement dressed up as a stylistic one.
It is not the same as a smile-friendly photo
A LinkedIn photo is the opposite case: a genuine, relaxed smile is standard there and generally outperforms a stiff neutral expression, because the platform rewards approachability over documentary consistency. Neutral expression is the right call for a resume photo submitted in a country that expects one, or for 1x1 and 2x2 ID photos — not for a professional networking profile.
Neutral does not mean tense
The most common mistake is over-correcting into a stiff, held expression. A relaxed jaw and soft eyes read as calm and neutral; a locked, unmoving face reads as tense, and reviewers notice the difference even if they cannot name it. Some fields, like litigation, deliberately choose a composed, serious expression over a smile for the same reason lawyers do — it is a choice, not a default to fall back into by accident.