According to Official Guinness Records,
The largest instant photo gallery consists of 40.383 Polaroid photos and was achieved by the Canton of Schaffhausen (Switzerland), in St. Gallen, Switzerland, on 10 December 1995. The event took place at the OLMA '95, a fair for agriculture and nutrition.
For a complete list of 1995 records, please visit 1995 Guinness Records in Switzerland.