This is a photo of five photographers holding a very heavy analog camera at arm’s length. Joseph Byron, founder of the Byron Company (a commercial photography studio founded in 1892 in Mnahattan), is holding the camera at the left, his colleague Ben Falk on the right. Pirie MacDonald, Colonel Marceau, and Pop Core are the photographers in between. This studio is still operating with the 7th generation of Byrons, Thomas Byron, and his son Mark running the business.
It’s clear in the photo below that one of the photographers stepped out of the picture to take a photo of how this first selfie was made. My guess it is the Colonel.