Pornhub is using facial recognition (and other methods) to index people in videos:

https://social.mikegerwitz.com/url/30018

The article brings up important points. Porn actors often have different identities. What about amateur/revenge porn? This is a much more intimate example of the privacy threats that already exist. People seem to care a lot more when it affects them on such an intimate level, even though this is already being done in non-pornographic settings.

I've been thinking for well over a decade about people who place themselves in porn videos---be it professionally, or just for fun---and how their lives will one day change when everything they have ever posted online, even if it was a lifetime ago, is indexed and searchable. Privacy can't be retro-active---technology is advancing at too great of a pace. By the time you know to be concerned, you've already lost. And there's nothing you can do about that.