Informative Caption swoops in to let us know:
Richard Burton and Claudia Cardinale smile in an amused attitude, while Elizabeth Taylor cries out, catched [sic] by the snapshot of the photographer: the three well-dressed stars enjoy a toast during a party at Vendramin Calergi Palace on the occasion of the 28th Venice Film Festival. Venice (Italy), 9 September 1967.
I’d merely add that I believe this is the photo that ran next to the entry for “cheers” in the dictionary from 1968-1984.