In accordance to the "Copyright Term and the Public Domain in the United States, 1 January 2009" [1] Images published with notice but copyright was not renewed from 1923 through 1963 are public domain due to copyright expiration. "El Imparcial" which went out of service over 35 years ago, could not have renewed it's copyright which expired. Therefore, since Puerto Rico fell under US copyright in 1947 as well as today, this would make the image public domain.
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 (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.