The proposed CSAM scanning used perceptual hashing to try to identify CSAM material known to law enforcement.
It was not a tool to identify private images as being underage. That’s an impossible task.
I'd say modern AI tools could probably do this pretty effectively. They're very effective at describing anything else about an image. I have a workflow that churns through large amounts of images, describes them, and then looks for things I specifically want (in my case, auction listings that are not described accurately on the auction website).
It's impossible to do with perfect accuracy, but that doesn't mean it isn't done.
Just ask the dad who was investigated for taking pictures of his toddler for the doctor: https://www.koffellaw.com/blog/google-ai-technology-flags-da...