Wisconsin Historical Society. The one on the left is Harold Gauer himself, but he's not the reason I'm posting this.
Who are the other three people apparently standing on the wall?
None other than Ray Bradbury's writer friends Robert Bloch, C.L. Moore and Henry Kuttner. The photo was apparently taken outside Bloch's parents apartment in Milwaukee, when husband and wife Moore and Kuttner were on a visit from California. The photo is undated.
Harold Gauer was a friend of Bloch's from high school, and the two collaborated on some fiction in the 1930s. In fact, Bloch's first published fiction was a story called "The Thing", which appeared in a magazine edited by Gauer. Gauer talks about Milwaukee and his escapades with Bloch in this interview from the Unofficial Robert Bloch site.
The Wisconsin Historical Society has many more Gauer photos of Bloch, many of them funny, quirky or just bizarre. Browse the complete set here.
Thanks to jkt for alerting me to the Gauer collection.