What size is a US passport photo?
2×2 inches (51×51mm), which is 600×600 pixels at 300 DPI. Head should be between 1-1⅜ inches from chin to top.
Can I use this for other country passports?
This tool creates US standard (2×2"). For other sizes: UK uses 35×45mm, EU uses 35×45mm. Adjust dimensions manually if needed.