The original photo used in the final scene of The Shining is shown in the film to be a 1921 photograph of a July 4th ball at the Overlook Hotel.
Of course, the Overlook Hotel isn’t real, and the photo isn’t even from Colorado’s Stanley Hotel. That said, most of the photo is genuine. The biggest exception being that Jack Nicholson was not in the original shot.
For the film, Stanley Kubrick’s team of photo retouchers, using an exacto blade, an airbrush and glue, placed Jack Nicholson's face onto the body of the man in the front of the photo. Kubrick carefully photographed Nicholson to match the lighting and angle of the original photo, and shot him from different distances to create an image size that would match the original's grain structure when enlarged.
The original photo was discovered in The Complete Airbrush and Photo-Retouching Manual by Peter Owen and John Sutcliffe, published in 1985.
The most recent breakthrough was a few days ago when redditor u/Al89nut identified the original man who Nicholson replaced as Santos Casani, a quite well known London-based dancer (and more specifically, instructor and author on the subject of ballroom dances like waltzes and tangoes). This is potentially very useful information as Casani's appearances at dance halls during the 1920s and later, giving lessons and demonstrations en masse, judging competitions, attempting to set records (he apparently tried to dance straight for 24 hours once) were often mentioned in newspapers and newsreels.
The fact that Cassini is in attendance, as well as other faces that were likely identified, leads people to believe this photo was taken in England. It is also assumed that the year was not 1921, but 1923 and based on the attire and the assumption the photo was not taken in the United States that the celebration was a New Years Ball, and not a Fourth of July soirée.