What are we verifying our ages for? Pornography, gambling and other 18-rated content isn't allowed on Tumblr in the first place
The "mature content" flagging system is notoriously inadequate:
"Mature content" flags have been observed incorrectly applied more frequently to content and blogs belonging to marginalised people (especially trans women and people of colour)
Content-less reblogs have been flagged as "mature content", while the original remains unflagged
Posts talking about racism, sexism, and other forms of discrimination have been flagged as "mature content"
Posts about the inadequacies of the mature content system have been flagged as "mature content"
Picture containing edited images of text (specifically "drowned" screenshots) have been flagged as "mature content"
Infamously, pictures of sand dunes have been flagged as "mature content"
Meanwhile, adverts on Tumblr are not subject to the same restrictions as posts
In addition to this, there is an inherent danger in uploading government ID online and encouraging it is encouraging users to take a significant risk with potential lifelong repercussions. k-ID has had data breaches in the past and will inevitably have them again, and using a social media website simply isn't worth the trade-off. I am not alone in saying that I would rather not use Tumblr than have my government ID exposed to the world.
As an alternative: Tumblr's ToS require users to be 13 or older. Any account that is over five years old can, therefore, be assumed to be owned by an adult. Failing that, users can make a one-off peppercorn payment in the TumblrMart using a credit card. Those methods are at least as accurate as an AI assessment of (what the user claims is) the user's face.
PS: I would actually like an answer to that first question - if age-restricted content isn't allowed on Tumblr, what does it matter whether we're over 18 or not? The UK law this is allegedly in response to is dated 2023, so "legal compliance" seems like a flimsy excuse.