Comment by Retr0id

It's a real shame Google isn't more transparent about how it actually works, and doesn't provide any mechanism for classifying images in bulk or offline.

This is the best SynthID write-up I've found so far: https://fyx.me/articles/attempting-model-extraction-of-googl...

It covers how it actually works (probably), and how to train your own classifier for it, with some seemingly decent results.