Document photo sizes, and how to read a specification

The US visa and Diversity Visa digital photo is square. It must be at least 600 by 600 pixels and no more than 1200 by 1200. It must be JPEG, 240 KB or less, in colour at 24 bits per pixel in sRGB, with a compression ratio of 20:1 or lower. If you are scanning a printed photo instead, the print is 2 by 2 inches, which is 51 by 51 mm, scanned at 300 ppi. The page is at https://travel.state.gov/content/travel/en/us-visas/visa-information-resources/photos/digital-image-requirements.html, and it carries example images no amount of text substitutes for.

The UK passport digital photo must be at least 600 pixels wide and 750 pixels tall, with the file between 50 KB and 10 MB. It must be in colour, in focus, against a plain light-coloured background, and not altered in any way. Those requirements are published at https://www.gov.uk/photos-for-passports, and that page is the only version of them that counts.

Two things are worth pulling out. Neither is the 35 by 45 mm rectangle people expect a passport photo to be: the US is square, and the UK digital rule is expressed as pixel minimums and never mentions millimetres. And both specify more than a size - a format, a colour instruction, and a file size range with a bottom as well as a top.

The table separates what was verified from what is merely common. Treat the last four rows as a description of what tends to be asked for, not as a rule you can submit against.

The 35 by 45 mm print size derives from the ICAO travel document standard and is the size most often quoted outside the United States - Schengen visa applications, Indian and Nepali documents and a long list of others are commonly described as using it. At 300 dpi it is 413 by 531 pixels.

It is not, though, any particular country's rule. Authorities that share a print size still differ on background colour, on how much of the frame the head must fill, and on what their online system wants, which is often nothing like the print size.

The UK is the clean illustration. A printed UK passport photo is usually given as the familiar 35 by 45 mm rectangle, while the digital application asks for at least 600 by 750 pixels and a file between 50 KB and 10 MB. Assume the print size is the requirement and produce 413 by 531, and you are under the digital minimum on both axes.

A print size describes ink on paper. A digital image has no physical size at all - it has a pixel count, and a pixel has no width until something decides to print it. The bridge between them is a resolution figure in dots or pixels per inch.

The conversion is one line. There are 25.4 millimetres in an inch, so pixels equals millimetres divided by 25.4, times the dpi. For 35 by 45 mm at 300 dpi: 35 divided by 25.4 is 1.378 inches, times 300 is 413.4, so 413 pixels wide. The height comes out at 531.5, so 531 tall. At 600 dpi the same rectangle is 827 by 1063.

Two notes on rounding. Fractional pixels do not exist, so round to the nearest whole one - but where a form states a minimum, round up, because 413.4 rounded down is short. And two inches is 50.8 mm, not 51. Specifications quoting 51 mm are rounding for convenience, harmless on paper and 602 pixels if you convert it literally.

JPEG files carry a density field, a note saying print me at 300 per inch. Photo editors display it, EXIF viewers display it, and specifications that say 300 dpi minimum have taught a lot of people to worry about it.

On a web upload it is almost always irrelevant. Changing that field from 72 to 300 adds no pixels and moves the file by a few bytes. Anything checking for detail counts pixels, because the pixels are the detail.

So when a specification says 413 by 531 at 300 dpi, read the pixel figure as the requirement and the dpi as an explanation of where it came from. Relabelling a 200 by 250 photo as 300 dpi complies with nothing, and a tool offering to raise your dpi without changing dimensions is selling you a metadata edit.

Two exceptions. If the photo will be printed, the tag tells the printer what physical size to make, so a wrong value puts the right pixels on the wrong-sized paper. And a few older systems built around scanners do read the field. If your form says so in writing, set it.

A photo specification answers a short list of questions, and it helps to know which answers are checked automatically and which by a person. The automatic ones are pass or fail in the second after you press upload. The human ones come back days later with a rejection letter.

The first group is mechanical, and software can produce it exactly. The second is photography, decided before the shutter. A cropping tool cannot see whether the wall behind you is evenly lit.

One pairing causes most of the failures: a minimum pixel size together with a maximum file size. They pull in opposite directions, and the obvious response - shrinking the image to get under the byte cap - fails the check that runs first. Crop the background out instead, since file size follows detail, then compress.

Head height rules get quoted wrongly more often than any other number here, partly because authorities express them in incompatible ways. Some give a millimetre range from chin to crown, some a percentage of the frame height, and some publish a diagram with two arrows and no numbers in the text.

Read that requirement on your own authority's page and compose to it when the photo is taken. It is the one thing you cannot fix afterwards. If the head was too small in the frame, cropping in throws away resolution you may need for a pixel minimum, and cropping out is impossible once the top of the head is at the edge.

Background is the same kind of problem. Plain and light-coloured is a photography instruction, not an editing one - replacing a background digitally is what unaltered rules exist to exclude, and the result tends to be detectable at the hairline. Stand a metre or so from a plain wall so your shadow falls behind you.

The routine is short. Find the requirements page on the issuing authority's own domain, not an aggregator and not a photo shop. Read it in full rather than skimming for the size, because format, colour and file size rules sit in separate sentences from the dimensions. Then check your file against every constraint, including the ones that are words rather than numbers.

Where the authority publishes example photos, look at them. They resolve questions the text leaves open - how much shoulder to include, how close is too close - faster than any written description.

If a specification is genuinely ambiguous, take the stricter reading. A photo at the higher end of an allowed pixel range and comfortably inside a file size window passes either way. One sitting exactly on both boundaries passes only if your interpretation matches theirs.