Everybody belongs to one of three facial types, if one will sort them in this concept
Betaface has some disadvantages like many face recognition engines. This includes not guessing ethnicity and gender of people right, using beards and hair styles as similarity indicator, or facial expression. It is good at comparing individual traits like nose and facial bone shape, but is far from being able to say if someone is Finnish or Basque. It also can do strange guesses by crossing the ethnic barrier. For example someone with a very board nose can be rated similar to Africans, or fat faced people and Trisomy21 can be rated as East Asian, because of their small eyes.
Facial recognition software is programmed by people, so it will reflect their own ratings and beliefs.
The same problem occurs with the older system of metrics.
Once there was a metric calculator for physical skull shape by Dienikes. It was able to calculate your skull shape in the old terms of Coons racial classification by measuring many facial variables. I measured many people in my social environment and they all came out different.
After all it stays a point of view which traits one or the machine/program is interpreting as more important as the other.
But there are many other things to consider why measuring ethnicity/race is so complicated. For example some alleles are dominant over others and some are recessive.
Lets imagine you would have two parents of completely different ethnic background. Many trait alleles would be heterozygote AG or TC for example. A simple PCA tells you that you would have to look 50% 50% like each parent. But in reality you don’t, because some traits are recessive and wont show up on your phenotype at all.
People want to know what ancient phenotype they have. But this is much more complicated then tracing ancestry. You can look more similar to a person that is not directly related to you, than to you own grand parents. But a machine can easily tell you today that they are your grand parents and not the person who looks more similar to you, but is not directly related to you.
Different people would rate the same person may not as the same ethnicity, when it comes to continental classifications.
But there are also people who cannot see a difference between a Papuan and a Nigerian, or cannot see difference in a Japanese and a Mongolian.
Different ratings of similarity are also present in other things:
https://www.eupedia.com/forum/threads/35849-Is-your-brain-more-Western-or-more-Eastern-part-1