The UK's passport photo checker system is biased against women with darker skin tones, according to a BBC investigation.

BBC journalists fed over 1,000 photos of politicians from around the world into the online checker, recorded the gender and skin tone of each photo using the Fitzpatrick skin-tone scale and analysed rejection rates across different skin tones and genders.

The broadcaster found that dark-skinned women were more than twice as likely to have their photos rejected as poor quality compared to light-skinned men, and that 22 percent of photos of dark-skinned women were rejected, compared to only 9 percent for light-skinned men. 

It also found that women with the darkest skin tones were four times more likely to have their images rejected than women with the lightest skin, and that the system incorrectly flagged issues like "open mouths" on photos of dark-skinned women when their mouths were clearly closed.

The investigation demonstrated how racism can be perpetuated through seemingly neutral technological systems. Experts suggested the issue likely stems from a lack of diversity in the training data used to develop the facial detection software.