I've been digging through the latest related commit in the repo: https://github.com/signalapp/Signal-Android/commits/master

They appear to use "com.google.firebase:firebase-ml-vision-face-model:20.0.1" to detect the faces.

The actual blur appears to be done here: https://github.com/signalapp/Signal-Android/blob/514048171bf...

Not sure what "ScriptIntrinsicBlur" stands for exactly, it appears to come from the android SDK itself: import android.renderscript.RenderScript;

EDIT: https://developer.android.com/reference/kotlin/android/rende...

It's a gaussian blur filter with a radius of 25px if I understand the code correctly.