Why passport photographs get rejected
Passport and visa photograph rejections are rarely about the photograph being bad. They are about measurements. Almost every authority specifies the head height as a proportion of the image, and that proportion is what an automated check measures first. The US requires the head to occupy between 50 and 69 percent of the frame height. The UK and the Schengen area measure the crown-to-chin distance in millimetres against a 45 mm tall print. India specifies a square photograph with its own ratios.
This is why cropping a nice portrait to the right pixel dimensions fails. Getting a 2x2 inch image at 600x600 pixels satisfies the file specification and says nothing about where the head sits inside it. A photograph where the head is too small, which is the usual mistake because people frame like a normal portrait, is rejected by a system that never looked at the image quality at all.
The second most common cause is the background. Requirements ask for plain white or off-white, evenly lit, with no shadow. A wall photographed with a flash produces a bright disc behind the head and darker corners, which is not an even background. A wall photographed without a flash usually produces a shadow on the side away from the window. Neither is a difficult problem to see once you know to look for it, and both are invisible to someone checking whether the picture looks nice.
Then there are the rules that are simply lists: no smile showing teeth for most authorities, eyes open and clearly visible, no glasses for many countries now, head straight rather than tilted, mouth closed, no hair across the eyes, no uniform, plain everyday clothing, and no head covering except for religious reasons with the full face still visible. Each one is a separate reason a submission comes back weeks later.
What this tool does is measure rather than guess. It works from the crop you place, computes the resulting head-height ratio against the specification you selected, and shows you the numbers you are being judged on before you submit. It cannot photograph you against a better wall, and it will not pretend that a rule about glasses is something software can fix.