>Fourth, this kind of voluntary search by the likes of Google is not unprecedented. Google scans outgoing Gmail messages to see if there are attachments whose hashes — that is, digital fingerprints — match those of known images of child pornography. When this first became widely known to the public, the company explained: “Sadly all Internet companies have to deal with child sexual abuse … It’s why Google actively removes illegal imagery from our services—including search and Gmail—and immediately reports abuse … This evidence is regularly used to convict criminals.”

>To be sure, child pornography filtering — and reporting — may be a place to draw a clear line. Not only is child pornography near-universally reviled and banned, but the matching algorithm for previously-identified images boasts no false positives, and, perhaps most important, possession of the file is not only clear evidence of the crime, but quite typically the crime itself.

I had no idea Gmail did this.