The general rule
Most countries want the head, from the top of the hair to the chin, to fill roughly 70 to 80 percent of the photo height, with the face centred and level.
US example
For the 2 × 2 inch US photo, the head should measure about 1 to 1⅜ inches (25 to 35 mm) from the bottom of the chin to the top of the head. The US passport photo maker crops to this layout.
Other countries
Sizes and head measurements differ for the UK, Canada and Australia, so use the maker for your country and compare with the official page.
Common framing mistakes
Head too small because you stood too far away, head tilted, face off-centre, cut-off hair or chin, and too much empty space above the head. Take the photo from about arm's length at eye level and crop afterwards.
Related
Passport picture checklist and how to take a passport photo at home.