The checkmark is the wrong approach. You should never trust accounts, because accounts get hacked. We should instead use cryptographic signatures on individual posts, and clients can warn when that signature doesn’t match the account’s public key, or if that key changed recently. The private key would never live on the server, and ideally live outside the app.

This doesn’t verify identity, it just proves the key didn’t change. To establish identity, the person needs to use the same key in multiple places, such as posting it on a personal website or something. If a service wants to add their own stamp of approval, they can sign these public keys and embed them into the apl for clients to use (e.g. show a blue checkmark if Bluesky can verify the public key outside its system).

If the private key is compromised, repeat the process, potentially signing the new key with both the old and new key to prove control of both (or start from scratch if needed). Repeat whenever they get hacked.