Reference pages first, if you are working on an ID, passport or visa photo: the twenty-destination spec matrix shows which frames are actually in use and where the background and head rules diverge, portal upload limits lists the pixel, KB and format ceilings enforced by the receiving systems, and the portal rule sets for the U.S. DS-160 upload, the UK visa upload, Canada's online renewal and Japan's square visa frame are transcribed in full.
How these guides are sourced
Every numeric claim on this site is quoted from a government or portal page, with the access date printed next to it, and every page names the artefact it came from rather than a summary of it. That sounds like housekeeping until you try to use the numbers: a great deal of what circulates about photo sizes is second-hand, and second-hand figures tend to be the ones that fail a form.
Three consequences follow, and they are the reason some pages on this site look different from the guides elsewhere.
Where two official pages disagree, the disagreement is printed. Canada's digital photo ceiling is stated as 4 MB on the specification page and 5 MB on the general requirements page. We publish 4 MB and say why on the page, rather than picking the more convenient number silently.
Where a figure could not be verified, nothing is written.
Japan runs an online visa channel whose upload ceiling we have not captured; that page states the gap instead of repeating a number from a blog. A page that admits what it does not know is more useful than one that invents a ceiling you will fail at 2 a.m.
Print specifications and upload specifications are kept apart. A 35 × 45 mm print exported at 300 DPI is 413 × 531 pixels, which is below the 600 × 750 pixel floor of the UK visa upload. Guides that quote one number for both send people into exactly that failure.
When a page here is wrong, the correction is applied and recorded on the change log; the standard itself is on the methodology page.
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