Start with the moment of submission. What will the form ask you to upload or hand over, and what exact checks can fail? Work backwards from those answers.
The measurement first
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.
Keep the file understandable
Use a destination-based filename instead of names such as IMG_1047.jpg. Clear naming is not an SEO trick; it is simply good operational practice when the same portrait appears in several application folders.
Keep the workflow reversible
Preserve the source image and make separate application versions. Reversible workflows are safer because a changed requirement does not force you to start with a damaged or repeatedly compressed file.
A note for this exact search
The safest reuse pattern is master first, derivative second. Never make a new country-specific output by repeatedly editing the last JPEG you exported.
Visa Photo File Size Guide
Upload your photo or take a new one, choose the destination profile and review the final file before you submit it.