Google isn’t the only service checking for csam. Microsoft (and other file hosting services, likely) also have methods to do this. This doesn’t mean they also host csam to detect it. I believe their checks use hash values to determine if a picture is already clocked as being in that category.
This has existed since 2009 and provides good insight on the topic, used for detecting all sorts of bad category images:
Google isn’t the only service checking for csam. Microsoft (and other file hosting services, likely) also have methods to do this. This doesn’t mean they also host csam to detect it. I believe their checks use hash values to determine if a picture is already clocked as being in that category.
This has existed since 2009 and provides good insight on the topic, used for detecting all sorts of bad category images:
https://technologycoalition.org/news/the-tech-coalition-empowers-industry-to-combat-online-child-sexual-abuse-with-expanded-photodna-licensing/