Google reports allegedly pornographic video involving children which has been uploaded to a Google Drive. When Google finds sexually exploitive material, they report such contraband to [the National Center for Missing and Exploited Children or NCMEC], and capture the IP addresses and account information. This information is given to local police who then obtain subscriber information of the IP address from the internet service provider and obtain a search warrant.
A tip from Google started detectives on a virtual chase through emails, phone records, social media and fetish sites that ended in the discovery of a trove of child pornography — and two arrests, including an Alberta woman accused of sexually assaulting her own young son.
Source: How internet detectives tracked a child porn trail from Idaho to Red Deer – Calgary – CBC News