US Passport & Visa requirements (2x2 inches / 600x600 px)
The US Department of State requires digital passport photos to be exactly 600x600 pixels (1:1 square ratio) with a minimum resolution of 300 DPI, white/off-white background, and file size between 10 KB and 240 KB.
Schengen & UK Visa requirements (35x45 mm)
European Schengen visa portals and UK Visas and Immigration mandate 35x45mm dimensions (roughly 413x531 pixels at 300 DPI) with the applicant face covering 70% to 80% of the vertical frame.
Indian passport & government exam portals (20KB - 50KB limits)
Indian government portals (SSC, UPSC, Passport Seva) enforce strict file size caps, commonly requiring applicant photos to be between 20 KB and 50 KB, and signatures to be under 20 KB.