PD-PRE1978. The photo has no copyright markings on it as can be seen in the links above. Note there is a collectors' or photographers' mark on the bottom of the photo's back. Close examination shows it is not a copyright mark.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.