Yes, the photo in RAISING KANE is the only one I know of Welles and Mankiewicz together, but I bet that there are some in old newspaper files in New York. After Welles gave Mankiewicz a job writing radio scripts for the Mercury Theater on the Air, they hobnobbed and nightclubbed together quite a bit.
In the photo in question, Welles appears in formal wear, and though he is smiling, looks uncomfortable, bemused. Mankiewicz, on the other hand, in a natty double-breasted suit and fedora hat, cigarette butt in two fingers, is sizing Welles up with a sly grin which suggests he has just consumed a mouse the size of a summer sausage.
Wonderful photo -- especially, considering what we know of the relationship.
Does anyone know the occasion?
The announcement of the Academy Best Original Screenplay nomination, perhaps.