The U.S. Department of State publishes exact technical specifications for digital photos submitted with visa applications on its “Digital Image Requirements” page. A photo that misses any of these mechanical rules can be rejected by the upload system before a human ever sees it.
Two failure causes deserve special mention because they are invisible to the eye. First, the spec requires the sRGB color space — but modern iPhones capture photos in Display P3 by default, so an unconverted iPhone photo can fail even though it looks perfect. Second, the 240 kB cap is small for modern cameras; a straight-off-the-phone photo is usually 10× that size.
The State Department also documents separate rules for scanning an existing printed photo: the print must be 2×2 inches (51×51 mm) and scanned at 300 pixels per inch.
Photo composition rules (head position, background, expression, glasses) are published on the same official pages and are checked by humans and automated systems — this entry covers only the file mechanics. Always review the official photo page for your specific application before submitting.