What's great about this group: Stay up to date on how this project progresses.
Update (22 April 2024)
According to the Guinness Book of records, the largest photo mosaic was created in Chongqing, China on 28 September 2022, with the help of 70 volunteers. It was 25,856.32 ft² and consists of 50,000 photographs. A previous record of 21645.96 ft² was set at a convention center in Tampa, Florida, on 11 October 2012 - and the photos (over 176,750) were crowd-sourced. I cannot find the associated Facebook group, though.