What is DPI — print resolution for photos
What DPI means for a passport photo: dots per inch, millimetres to pixels, and 300 vs 600 DPI.
DPI (dots per inch) is how many pixels sit in one inch of print. A 35×45 mm photo at 300 DPI is about 413×531 pixels. At 600 DPI the file is four times the pixels.
Screens do not use DPI the same way printers do. For a visa form, 300 DPI is the usual lab request. The passport studio converts millimetres and DPI to pixels locally.
DPI is dots per inch, a print density. 300 dpi is a common photo-print target. A 35×45 mm frame at 300 dpi is about 413×531 pixels. The same pixel file tagged 72 dpi is not smaller on screen; the tag mostly matters when a program converts pixels to centimetres. This page defines the density. The passport tool uses it to size the frame.
FAQ
Is 72 DPI enough for print?
No. Labs ask for 300 DPI. 72 is a screen convention, not a print spec.
Does a higher DPI make the photo sharper on screen?
On screen you just see more pixels. Sharpness in print needs both DPI and a sharp source.