Comedian and game show host Jan Murray has his hand on Dean Martin's
shoulder in this photo.
The poster was made from a photograph which is described as follows:
"Rat Pack at Carnegie Hall
Jan Murray (L) sits alongside Rat Pack members Dean Martin, Sammy
Davis Jr., and Frank Sinatra as the group unwinds backstage at
Carnegie Hall after entertaining at a benefit performance in honor of
Dr. Martin Luther King Jr.
Date Photographed: January 27, 1961
Location Information: Manhattan, New York, New York, USA"
Corbis: Rat Pack at Carnegie Hall
I've enlarged a section of the photo, and you can see that the hand
belongs to Jan Murray (who has his arm around Dean Martin), not to the
unidentified man standing in the background:
My strategy in locating this information began with a search on the
Corbis site, which has a huge archive of commercially available
photographs. I thought I remembered having seen the Rat Pack boys in
this pose in a photo at Corbis, and once I located the photograph
(with the caption that mentioned Jan Murray), things fell into place.
I hope this is precisely what you need. If anything is unclear or
incomplete, please request clarification; I'll be glad to offer
further assistance before you rate my answer.