Head height and eye line explained
Passport specifications are written in a vocabulary nobody uses anywhere else: crown, chin-to-crown, eye line from the bottom edge, seventy to eighty per cent of the frame. Each term describes one measurement, and together they decide where your face sits in the rectangle. Understanding them is the difference between cropping by eye and cropping to spec.
Chin to crown, and the 70–80 per cent rule
Head height means the distance from the bottom of the chin to the crown — the top of the skull, including hair. Not the hairline, not the eyebrows, not the top of the forehead. ICAO Doc 9303 expresses the requirement as a proportion: the head should occupy about 70 to 80 per cent of the frame height. On a 45 mm print that gives roughly 31.5 to 36 mm, which is where the familiar 32–36 mm band comes from. Countries then publish their own narrower ranges — 29 to 34 mm in the UK, 34 ± 2 mm in Japan — and those take priority over the general proportion.
The eye line, used by the US and India
Some authorities fix the vertical position of the face directly rather than through the head. The United States requires the eye line — an imaginary horizontal line through the centre of both eyes — to sit 1⅛ to 1⅜ inches (28.6 to 34.9 mm) above the bottom edge of the print, in addition to a head height of 1 to 1⅜ inches. India specifies 28.5 to 35 mm on its 35 × 45 mm photo. This matters because two crops with an identical head height can place the eyes at different heights, and only one of them passes.
Clear space above the head
A third rule appears in some standards: a minimum margin between the crown and the top edge. A Chinese visa photo requires at least 7 mm; Russian interior ministry orders specify about 5 mm. Without it, a technically correct head height can still be cropped so tight that the head touches the edge. Where a country publishes such a margin, ID Photo checks it as a separate line in the report rather than folding it into the head measurement.
How the measurement is made — and when it is only an estimate
The app locates facial landmarks, finds the chin and the crown, and converts the distance into millimetres for the frame size you selected. The chin is easy; the crown is not, because hair has no hard edge and may be cut off by the original photo. So the report says where the number came from. If the top of the head is outside the original frame, that is a failure and no crop can fix it. If the crown had to be estimated, or hair made it ambiguous, you get a warning rather than a clean pass — because a head height derived from a guessed crown is a guess, and it is more useful to know that before you print.
Frequently asked questions
Where exactly is the crown of the head?
The top of the skull as it appears in the photo, including hair. It is not the hairline or the top of the forehead, which is why voluminous hair genuinely changes the measurement.
What does “head must be 70–80 per cent of the photo” mean?
That the chin-to-crown distance should be 70 to 80 per cent of the frame height. On a 45 mm tall photo that is about 31.5 to 36 mm.
What is the eye line?
A horizontal line through the centre of both eyes. The US and India specify how far it must sit above the bottom edge of the print, which fixes the vertical position of the face independently of head height.
Why does the app warn that the crown was estimated?
Because the top of the head was not clearly visible — usually hair without a defined edge, or a head cropped close to the frame edge. The head height then rests on an estimate, and you should know that before printing.
Can a photo have the right head height and still fail?
Yes. If the country also specifies an eye line or a minimum margin above the head, a correct head height placed too high or too low in the frame still fails.
Does the measurement change if I choose a different country?
The physical photo does not change, but the target range does, so the crop does. Switching from the ICAO template to the UK standard, for example, narrows the acceptable head height from 31.5–36 mm to 29–34 mm and re-crops accordingly.
Measure the photo before the counter does. ID Photo opens your picture in the browser, measures head height and eye line against the official spec of the country you pick, and lays out a print sheet. The image is processed on your device.
Measure a photo in the browser