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In every reported case where police mistakenly arrested someone using facial recognition, that person has been Black
(www.businessinsider.com)
This is a most excellent place for technology news and articles.
It's not just a training issue. Lighter (color) tones reflect. Dark tones absorb. There have been lots of issues with cameras or even just sensors having issues with people having dark skin tones because the lower reflectivity/contrast of dark tones. 3D scanners - even current models - have similar issues with objects having black parts for similar reasons. Training on more models can help, but there's still an overall technical difficulty to overcome as well (which is also a good reason that using facial recognition in this manner is just bullshit, period).
As a technological problem it could have a technological partial solution: the darker the skin, the higher the threshold to declare a match. This would also mean more false negatives (real matches not caught by the software) but not much to do about that.