What the specification means in practice
The square 51×51 mm format is unusual — most of the world uses a 35×45 mm portrait rectangle — so a photo cropped for a UK, Schengen or Japanese application will not pass for a US passport, and vice versa. Head height is measured from the bottom of the chin to the top of the head including hair, not to the hairline, which is why a high bun, a beehive or thick volume on top can push an otherwise perfect photo out of tolerance.
How the head height is actually measured
The State Department expresses the requirement two ways and both appear in its own guidance: the facial image must be no less than 1 inch and no more than 1 3/8 inches, and equivalently between 50% and 69% of the total image height. The measurement runs from the bottom of the chin — excluding facial hair — to the top of the head, and the top of the head means the crown of your hair as it sits in the photo.
That tolerance sounds generous, but the two ends of it fail for opposite reasons. Too small and the passport agency cannot identify you reliably at the size the photo is printed in the book; too large and there is not enough margin to crop the image down to the 45×35 mm frame the passport itself uses. A face filling almost the entire frame can also introduce the barrel distortion the department calls fish-eye, where the nose and centre of the face are exaggerated relative to the ears.
Glasses are no longer accepted
This is the single biggest change to US photo rules in recent years and still the most common reason applications are put on hold. Eyeglasses must be removed for both passport and visa photos. The only exception is a medical one — recent eye surgery, for example — and it requires a signed statement from a medical professional submitted with the application. Ordinary vision correction is not a reason.
If you do submit a photo under the medical exception, the frames must not cover any part of the eye, there must be no glare on the lenses, and no shadow or refraction that obscures the eyes. In practice that is difficult to achieve with a phone flash, so shoot in soft daylight instead.
Background, clothing and expression
The background must be plain white, off-white or light-coloured, with no large shadows, reflections or objects behind you. Stand about a metre away from the wall rather than against it — that gap is what stops your own shadow falling on the background.
Wear what you wear on an ordinary day. Uniforms are not accepted, and neither is camouflage-patterned clothing, even as a whimsical print on a child. Religious clothing worn daily is fine. Hats and head coverings are refused unless worn daily for religious purposes, and even then your full face must be visible with no shadow cast across it. Headphones and wireless earpieces are never acceptable.
The expression must be neutral with both eyes open. A closed-mouth natural smile is generally tolerated, but anything that changes the shape of your face — a wide grin, raised eyebrows, a squint — risks rejection because it interferes with the facial recognition systems used at the border.
Printed versus digital submission
A paper application needs one printed photo on photo-quality paper. Online renewal requires a digital image instead, and the same 50–69% head-height rule applies to it. The photo must be taken within the last six months so that it reflects how you currently look — a photo reused from a certificate of citizenship often fails this test even when the certificate itself is recent, because of the processing time behind it.
Do not retouch, smooth or filter the image. Removing a blemish or softening skin is treated as a digital alteration, and photos with visible pixellation from over-compression or upscaling are refused outright.
Common reasons US photos are rejected
In rough order of frequency: eyeglasses; shadows on the face or the background; head size outside the 50–69% band; a background that is not plain; and photos that are simply too old. Two further ones catch people out — a head tilted or turned away from square to the camera, and photos taken as a selfie at arm’s length, where the short subject distance distorts facial proportions. Have someone else take the photo from about a metre and a half away, or use a timer.