Make a passport photo that meets the spec
Pick the document, drop a phone photo, and get a file sized to the exact millimetres at 300 dpi — plus a 4 × 6 inch sheet you can print anywhere.
What the tool does, and what it cannot
Consulates publish two numbers: a physical size in millimetres and a head height as a fraction of the frame. This tool handles the first completely, and the second approximately — it centre-crops, which puts the head in roughly the right place for a normal portrait but will not rescue a photo where you are at the edge of the frame.
It also sets the file to 300 dpi, so a print comes out at the right physical size. That detail is invisible on screen and is the single most common reason a technically correct photo gets rejected at a print shop.
The 4 × 6 inch print sheet button tiles as many copies as fit on a standard photo print — usually six for a 2 × 2 inch photo. Take that file to any pharmacy or print kiosk, choose 4 × 6 and glossy, and cut them apart. It costs a fraction of a dedicated passport photo service.
What gets rejected most often
In order of how often it happens, the reasons a photo fails are: a shadow behind the head, a background that is not plain, glasses with glare, a smile, and a head that is too small in the frame.
Shoot against a plain wall, stand a metre from a window so the light is even, and have someone else take the photo from slightly below eye level. Most phone cameras now produce a file that is more than good enough — the problem is almost never resolution.
Head height rules vary by country but cluster around 70–80% of the frame. If your document demands a specific head height, check the number on the form and leave margin around the head when you crop.
Questions
Can I use a selfie?
For most documents, no — the angle and the arm's-length distortion are visible. A photo taken by someone else at 1.5 metres is much safer.
What background do I need?
Plain white or off-white for almost every document. Some countries accept light grey or light blue; check the form. A shadow on the wall is the usual failure.
Does it remove the background?
No. It crops and sizes only. A background remover tends to leave halos around hair that fail automated checks.
Is the print sheet really 4 × 6 inches?
Yes — 1200 × 1800 pixels at 300 dpi. Choose the 4 × 6 option at the kiosk, not 'fit to page'.
Can I use this for a visa rather than a passport?
Yes, if the spec matches. Pick the country from the list; if yours is missing, use the closest millimetre size and check the head-height rule separately.