I assume it's mostly the same thing that keeps non-Catholics from taking communion at Catholic mass.

Note that I'm not a blacksky member, just someone involved in the greater atproto space so my understanding of the process is likely not perfect.

But AFAIK the way blacksky operates is that they assume good faith when new users join. If it becomes obvious that you are not black then you will likely get reported or directly hit by moderation action and they will ask you to verify your identity at some level.

I think it's something along the lines of "send a photograph that would be non-trivial to fake". Not necessarily forcing you to dox yourself but requiring that you provide some level of evidence that's visibly resistant to AI/tampering. Now I have no idea the extent to which they do this to be entirely honest but I do know they don't mess around with people doing "digital blackface".

I'm not sure how well that moderation approach will scale at large but given they are a community that has carved out their own niche and not a corp just blindly driving to scale, I doubt they'll see the strain that the greater bluesky and atproto have experienced with moderation struggles at scale. And given all decisions around policy and moderation rules are decided by the Blacksky People's Assembly, as the community evolves participants can participate in governance and help craft the process if they are dissatisfied.

I don't exactly know either, but it's probably some sort of lax verification measure like a selfie.

Don't need extreme measures to keep bad actors out if you're able and willing to throw out anyone who obviously doesn't intend on playing nice.