Women with darker skin are more than twice as likely to be told their photos fail UK passport rules when they submit them online than lighter-skinned men, according to a BBC investigation.
One black student said she was wrongly told her mouth looked open each time she uploaded five different photos to the government website.
This shows how “systemic racism” can spread, Elaine Owusu said.
The Home Office said the tool helped users get their passports more quickly.
“The indicative check [helps] our customers to submit a photo that is right the first time,” said a spokeswoman.
“Over nine million people have used this service and our systems are improving.
“We will continue to develop and evaluate our systems with the objective of making applying for a passport as simple as possible for all.”
The passport application website uses an automated check to detect poor quality photos which do not meet Home Office rules. These include having a neutral expression, a closed mouth and looking straight at the camera.
BBC research found this check to be less accurate on darker-skinned people.
More than 1,000 photographs of politicians from across the world were fed into the online checker.
The results indicated:
Dark-skinned women are told their photos are poor quality 22% of the time, while the figure for light-skinned women is 14%
Dark-skinned men are told their photos are poor quality 15% of the time, while the figure for light-skinned men is 9%
Photos of women with the darkest skin were four times more likely to be graded poor quality, than women with the lightest skin.