Ryan: "There's where it starts. Google logged the file upload time, IP address, and emails. They are using a file "fingerprinting" scanner."
DVD of account prepared for the police. Ryan: "The detective is reading through the guy's emails. It includes many other things, including details of his sister, but this is interesting."
Ryan: "He got a back and forth from a guy that Rick was in a sexual relationship with, skimmed over all their messages, and was able to note that they would frequently discuss young boys."
Ryan: "The detective is fishing based on what he found in the exchange between Rick and David through the emails that Google sent as part of the DVD contents."
Ryan: "He gets Rick to admit the whole thing."
More on sending the illegal material. Ryan: "The Express Stop photos aren't of interest with the Google thing, because they found those in his house with the Windows computers and hard disks and CDs and stuff."
Ryan: "They feed all of the images in and see what comes back as a hit for child pornography from the National Center for Missing and Exploited Children."
Ryan: "The additional material they found is catalogued and new material is submitted for inclusion into the database. The hashes are then shared with Google (and presumably others, like Microsoft OneDrive/Outlook, Apple iCloud) to train their detection systems, which is how Rick got himself reported in the first place."
Ryan: "Since they caught Rick and found his trove of tens of thousands of child porn images/videos, they can now find anyone else who has a copy and has put them into a monitored cloud storage or email system."