Almost every authority that issues passports permits head coverings worn for religious or medical reasons. What none of them permit is a covering that hides part of the face - and that single condition resolves nearly every question people have.
The condition
The full face must be visible: from the bottom of the chin to the top of the forehead, and from edge to edge across the face, including both ears where the authority asks for them. Nothing may cast a shadow across the features.
A hijab, turban, kippah, headscarf or medical covering that leaves the face clear satisfies this. A niqab or veil covering the mouth or chin does not. A covering pulled far enough forward to shadow the eyes does not, even though the garment itself would be acceptable worn differently.
What "religious or medical" means in practice
The permission is for coverings worn routinely - as part of religious observance, or for a medical reason such as hair loss during treatment. It is not a general permission to wear a hat.
Ordinary hats, caps, hoods and fashion headbands are refused everywhere, and this trips up more applications than any of the genuine cases.
Some authorities ask for a supporting statement with a medical covering, and a few ask for one with a religious covering too. That is a paperwork question rather than a photographic one - the official page for the document is where to check whether your application needs it.
Practical points when wearing a covering
- Set it back from the hairline. The forehead has to be visible. Pushing the covering back a few centimetres solves most refusals in this category outright.
- Watch for shadow. A covering with any structure at the front - a stiff edge, a fold, a turban wrap - can throw a shadow across the eyes under overhead light. Light from the front rather than above removes it.
- Keep the jaw line visible. A scarf wrapped high under the chin blurs where the face ends, which matters for the same reason background contrast does.
- Mind the head height measurement. Chin to crown is measured to the top of the head. A tall turban or a raised wrap can push the measurement beyond the allowed band, which is a separate failure from the covering itself.
- Contrast with the background. A white or light covering against a white background loses its outline. Where the document permits a grey background this is easier; where it demands white, the edge still has to be findable.
Wigs, hairpieces and hair loss
Wigs and hairpieces are generally acceptable provided the face is unobstructed and the appearance is your usual one. The guidance most authorities give is consistency: the photograph should look like the person who will present themselves at a border, so if you wear a wig every day, wear it in the photograph.
Hair loss from treatment is treated the same way as any other medical circumstance - a covering is permitted, and the face must still be visible.
What the checker can and cannot tell you
Software can measure whether the face is unobstructed, whether shadows fall across it, and whether chin-to-crown is inside the allowed band with the covering on. It cannot decide whether a particular garment qualifies as religious or medical for a particular authority - that is a judgement made by the office processing the application, against their own published wording.
IDShot measures the first set and links to the authority's page for the second, which is the honest division of labour between an app and a government office.
Requirements are changed by the authorities that publish them, and the official page is the only source that settles an argument. Each preset in IDShot links to that page, so you can confirm the current wording before you submit.