The publicity release is not dated. The program was on NBC from 1966 to 1969. The type of logo used on the NBC Press Release is the "second peacock", which was used by the network during the years 1962 to 1975. This would be in keeping with the timeframe the show aired on the network and also within the pre-1978 guidelines.
Because I couldn't view the back of this photo, I conducted various copyright searches on the UPenn site to try determining if any copyrights had been registered.
I searched the complete volumes for film and artwork for the years 1965 to 1969. Desilu Productions registered only w:The Lucy Show and w:Yours, Mine and Ours (1968 film) in conjunction with Walden Films. NBC registered only one still image-a color slide from Bonanza of Ben Cartwright on a horse.
Nothing turned up when I searched Star Trek for the years 1965 through 1969 in either film or artwork.
There's no evidence of copyright for this time frame from either production company.
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.