There are two separate questions here: “Can I make this image?” and “Will the authority accept it?” Good preparation answers the first without pretending to control the second.
Keep the units straight
Millimetres and inches describe physical output; pixels describe digital dimensions; DPI connects pixels to physical size during printing. If an authority already states the required pixel dimensions, use them directly. If you are building a print file from millimetres, the basic relationship is pixels = millimetres × DPI ÷ 25.4.
Where calculations stop being enough
A mathematically correct file can still fail because the face is the wrong size inside the frame, the background is unsuitable, the compression introduces visible artefacts, or the application expects a different file type. Finish every conversion with a visual and application-specific check.
Compress after you have the right dimensions
If a portal has a strict maximum file size, do not start by shrinking the image dimensions. First make the crop and pixel dimensions correct; then use JPEG quality or another allowed compression method to reduce the file. Re-open the compressed file and check for blockiness or ringing.
Keep a larger master
Save the original and a clean master separately. That way, if one portal needs 240 KB and another accepts a larger file, you can create both versions without repeatedly recompressing the same JPEG.
Authority-specific checkpoints
- U.S. passport photos are 2 × 2 inches (51 × 51 mm) and the head is expected to be 25–35 mm from chin to top of head.
- The Department of State says passport photos must be original and unchanged, including no software, app, filter or AI alteration.
Keep the requirement beside the file
Save the official page or instruction note with your application records when the task matters. Requirements change, and your future self should not have to reconstruct which version of the rules you followed.
Re-check the same pages before submission if the application is time-sensitive.
What the U.S. rules teach you to check
U.S. passport and visa guidance is a good reminder that “size” is only one layer. The passport workflow uses a physical 2 × 2 inch output with a head-size range, while many digital visa workflows introduce pixel, colour-space and file-size limits. That means a single portrait may need two technically different exports even when the subject and pose are unchanged. The sensible approach is to keep the original master and build the application-specific file at the end.
The U.S. Department of State also makes an important distinction between preparing a crop and altering the person’s appearance. A crop or resize can be mechanical; changing facial features or using AI to transform the appearance can cross a line the official guidance does not permit. When in doubt, fix the capture rather than “fix” the person.
What to remember from this page
For a family or multi-document job, label each output with both person and destination. It takes seconds and prevents mix-ups when several similar photographs are sitting in the same folder.
US Passport Photo File Size Guide
For print workflows, create the measured sheet and verify the physical output before producing the final batch.