What the specification means in practice
France uses the standard 35 × 45 mm frame with the face at 32 to 36 mm from the bottom of the chin to the top of the skull, excluding hair — which the guidance also states as 70% to 80% of the photo. Two details differ from what most applicants expect. Only one photo is required for a passport or ID card application, where many countries want two. And the background is specified as plain and light-coloured: light blue or light grey.
The background is not white
Light blue (bleu clair) or light grey (gris clair) is what the specification names. This trips up applicants who have just made a photo for a US, Indian or Korean application and assume white is universally safe. It is not — a white background here is outside the stated requirement.
The photo must not be over- or under-exposed, must be correctly contrasted, and must have no shadow cast on the face or on the background. Colour is strongly recommended over black and white.
Measuring the face to the skull, not the hair
The 32 to 36 mm measurement runs from the bottom of the chin to the top of the skull excluding hair (hors cheveux). That phrasing matters. The United States measures to the top of the head as it appears including hair; France measures to the skull underneath it.
For anyone with volume on top — curls, an updo, thick hair — those two conventions give measurably different results from the same photograph. Framing to the American rule will put a French photo below the 32 mm floor.
Six months, and it must still look like you
The photo must have been taken less than six months ago and must be a good likeness (ressemblante). The second condition is separate from the first: a photo taken four months ago that no longer resembles you, after a substantial change in appearance, does not satisfy it.
Glasses are optional
You are not obliged to wear glasses in the photo even if you wear them daily. If you do wear them, the frames must not be thick and must not mask the eyes, and the lenses must not be tinted or coloured.
Given that the simplest way to satisfy all three conditions is to take them off, and there is no requirement to wear them, removing them is usually the path of least resistance.
Where to have it taken
French photos for identity documents are typically made at an approved photographer or an approved booth (cabine agréée), and the public service site provides a search tool for finding one nearby. The same photo specification serves both the passport and the national identity card, so a single sitting covers both applications.