Short answers, pulled from the story.
Google announced Google Photos in May 2015 as a standalone service spun off from its social network, Google+. The company had launched Google+ to compete with Facebook but found it lacked the user base needed for photo sharing. By decoupling the photo features, Google transformed them from a sharing platform into a private library system.
On the 1st of May 2016, the closure of the Picasa Web Albums service followed after Google announced the discontinuation of the Picasa desktop application by the 15th of March 2016. Google stated the primary reason was to focus efforts entirely on a single cross-platform web-based service called Google Photos.
Google Photos shares fifteen gigabytes of free storage space with other services like Google Drive and Gmail. Users upload photos and videos in either original or compressed quality settings that count toward the free tier, though items uploaded before the 1st of June 2021 remain unlimited if taken via Pixel phones released before that date.
The service reached the one billion user mark in 2019 four years after its initial launch. In November 2020 announcements revealed more than four trillion photos stored globally with twenty-eight billion new items uploaded weekly.
John C. Dvorak of PC Magazine raised privacy concerns about Google's motivations and government relationships. He worried potential laws might require providing entire user photo histories upon request comparing it to inviting others to scrounge through underwear drawers.