The familiar scene at a submissions counter is somebody holding a complete folder, every signature in place, every stamp collected, being turned away over one photograph glued to the top corner. Wrong size, taken years ago, or on a blue background where the office wanted white.
The maddening part is that standing there you cannot tell who is right, because the clerk is repeating the habit of that particular office while you are repeating what the photo shop down the lane told you. It turns out only a small part of all those rules is actual regulation, and the rest is custom.
Most of what gets called an ID photo rule is not one
Go looking for the law requiring a job application to carry a 3x4 or a 4x6 photo and you will not find it, for the simple reason that no such law exists. Photo sizes for applications, for school enrolment forms, for staff badges are the habit of whoever receives them rather than legislation.
Real regulation covers only a few state-issued documents, most clearly the passport, plus visas where each country writes its own standard. Outside those two groups the useful question is not what the rule says but what this particular office wants, and only that office can answer it.
None of which is licence to improvise. ID photography has a very stable set of conventions, and following them gets a folder through almost any door.
Three familiar sizes and the pixels behind them
Vietnamese ID photos revolve around three sizes, quoted in centimetres because that is how photo shops name them. The 2x3 turns up on student cards and smaller passes, the 3x4 is the one most application forms expect, and the 4x6 is for passports and anywhere a face needs to be clearly readable.
To find out how many pixels a file needs, divide the centimetres by 2.54 and multiply by 300, since 300 DPI is the point where a print stops showing dots. That gives roughly 236 x 354 pixels for a 2x3, 354 x 472 for a 3x4, and 472 x 709 for a 4x6.
Those numbers are small enough that any phone has resolution to spare, so what falls short is almost never detail but proportion. The 3x4 happens to land on exactly the 3:4 a phone already shoots, while 2x3 and 4x6 are both 2:3, and a 9:16 upright frame matches none of them, so every picture has to be cropped before it goes to print.
Worth remembering too is that 300 DPI only means anything if you are printing. A file uploaded to a government portal carries no physical size at all, since the receiving end reads pixels and file weight and nothing else, which makes the arithmetic a waste of effort at that step. Converting centimetres into pixels at a given dot density is for the times you genuinely are going to a print shop.
For a national ID card, your own photo cannot be used
This is where a lot of effort gets wasted. Under Vietnam's 2023 ID Card Law, the officer handling your application collects biometric information on the spot, including the facial photograph, fingerprints and iris scans, so a photo you brought along cannot be printed on the card.
The portrait printed on the card is a standard 20 x 30 mm, which is the familiar 2x3, except that this is the issuing office's business rather than something you have to prepare. Your part is dressing tidily and turning up on time.
So if somebody tells you to get a set of ID photos taken before applying for a card, check before paying for them.
The passport is where the rules really are strict
Passport photos, by contrast, come with a document behind them. Under a circular issued by the Ministry of Public Security in 2023, the photo must have been taken within the previous six months, at four by six centimetres, facing straight ahead, with a bare head, both ears visible, no glasses, respectable clothing and a white background.
Every one of those lines exists for a mechanical reason rather than as etiquette. A face matching system needs the outline of the face and both ears, a white background separates the subject from whatever is behind them, and the six month limit keeps the photo resembling the person standing at the counter.
Visas vary by country and are often stricter still, with some demanding a square photo and others specifying the height of the face in millimetres. Before shooting for an application abroad, read that country's own page rather than a photo shop's blog post.
A white background is better shot than cut out
The easiest route to a white background is standing in front of a flat white wall, an arm's length away so your shadow does not land on it. Keep the light in front of your face, ideally daylight from a window, since a ceiling lamp carves dark hollows under the eyes and the chin.
Software can also produce a white background, and the place it shows is the hairline, especially the loose strands standing away from the head. Nobody inspects an internal form, whereas a document going through a machine reader can have a raggedly cut hairline treated as evidence of editing.
If you do need to cut one out, whether the strands of hair survive is what separates a good tool from a passable one, and remember to export onto solid white rather than leaving the background transparent, since a transparent file lands on black in a good many places.
There is exactly one case that forces a replacement, which is an office asking for a blue background or quoting an exact colour code you have no backdrop for at home. Picking the right background colour for a submission then matters more than the hairline does, because the wrong colour is refused at the counter rather than caught later under scrutiny.
Setting it up at home
Put the phone at eye level rather than holding it up at arm's length, because a high angle distorts the face and reads instantly as a selfie. Propping it on a stack of books and using the timer is enough, at about a metre and a half so the lens does not stretch your nose.
Keep the shoulders square and facing the camera, tuck hair behind the ears if the document wants them visible, and take glasses off to be safe. Keep the expression neutral with the mouth closed, since this is not the place for a broad smile, and the solemn face in official documents is an inheritance from a century ago.
Shoot plenty and pick afterwards, because an ID photo follows you around inside some folder for years. Cropping to the exact ratio comes after the shooting rather than during it.
How many prints come off one sheet
Photo shops charge by the sheet rather than by the picture, so knowing what a sheet holds tells you what you are paying for. A 10 x 15 centimetre sheet, the most common size of all, takes nine 3x4 prints in three rows of three, or four 4x6 prints in two rows of two.
Which means a set of nine 3x4 photos costs exactly one sheet. Needing only two for a form still costs the whole sheet, so print the full set and keep the rest for later, as long as they stay within whatever age the receiving office accepts.
The arithmetic of how many copies each paper size holds works identically for ID photos, only with different numbers.
Submitting online usually snags on file size
Government portals and recruitment forms tend to set two conditions at once, JPG format and a file under some limit, often a few hundred kilobytes. A photo from a recent phone weighs several times that.
The right order is cropping to the ratio first, reducing the dimensions to the pixels actually needed, and only then compressing under the limit. Doing it backwards, compressing an enormous photo and cropping afterwards, throws quality away twice and still may not pass.
On an iPhone there is one more step, since photos are saved as HEIC by default and most submission portals will not take it, so it has to become a JPG before upload.
The photograph you choose least and use longest
Looked at whole, an ID photo is one of the few pictures where you pick neither the moment nor the expression, and it never gets posted anywhere. In exchange it sits in a wallet, in a folder, in some office's system for years.
Which makes fifteen minutes of doing it properly once worth spending: a white wall, light in front of you, several frames to choose from, then a crop to the right size and the original filed away. Next time something needs one, you open a folder instead of a shop door.