I've often wondered why with the prevalence of Echo, Google Assistant, and engines that recognize what copywritten song you're using in a YouTube video... They haven't extended the code on our phones to listen for the sound signature of anyone watching a well-known child abuse video. Surely if they use the microphone they can get a lot more positives. Instead of just catching people who watched it on the phone direct…
Isn't it pretty rare for people to watch porn with the sound on?
Speaking as a frequent consumer of legal and ethical porn, I almost never turn the sound on. It's easier to contain leaks of light than of sound.
You can cast that net, I just doubt it'll catch many fish.