That precedent was set many years ago.

>a man [was] arrested on child pornography charges, after Google tipped off authorities about illegal images found in the Houston suspect’s Gmail account.

Microsoft’s “PhotoDNA” technology is all about making it so that these specific types of illegal images can be automatically identified by computer programs, not people.

PhotoDNA converts an image into a common black-and-white format and size the image to a uniform size, Microsoft explained last year while announcing its increased efforts at collaborating with Google to combat online child abuse.

https://techcrunch.com/2014/08/06/why-the-gmail-scan-that-le...