What is DPI?
DPI means dots per inch—how many ink dots a printer places along one inch of paper. It is a print concept, not a magic quality knob for screens.
A passport photo marked 300 DPI at 2×2 inches needs enough pixels (about 600×600) so the print stays sharp. Changing a DPI metadata tag without adding pixels does not invent detail.
For web delivery, pixel width/height and file size matter more than the DPI field in EXIF.
Related tool: Image DPI Converter