You can estimate age from images of the user's face (taken via webcam/front-facing camera). It wouldn't work well right at the threshold: you can't reliably dif

You can estimate age from images of the user's face (taken via webcam/front-facing camera). It wouldn't work well right at the threshold: you can't reliably differentiate 17 year olds from 18 year olds, but you can reliably keep the 10 year olds out. Or at least make a reasonable effort to do so, clever teenagers will find workarounds involving pictures or Halloween masks. This method doesn't seem to be allowed by the law in question though.