Jim Townsend wrote
In a JPEG file, the DPI setting is nothing but 5 bytes at the
beginning of the image data.
[Snip Long explanation and sample code]
That works for JFIF, but some (most, maybe? I don't know) digicams does
not add the JFIF block and instead uses EXIF. It's a lot more tricky to
tamper with the EXIF block.
I use dEXIF (Pascal only). I'm sure that there's freely available code
for other languages too.
Since you can always override the DPI settings at the time of
printing, there *really* is no point in changing it.
If the vertical DPI is different from the horizontal, maybe some
programs will assume that the image has another aspect than the one
corresponding to the size in pixels?
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