This image is in the public domain in Denmark because the DanishConsolidated Act on Copyright of 2010 specifies (§91, 5) that all photographic images not considered to be "photographic works" that were created before 1 January 1970 are exempt from protection (details).
Note that "photographic works", which must display artistic merit or originality, enter the public domain 70 years after the death of the photographer and that photographs that are not considered works but created 1 January 1970 or later become public domain 50 years after they were created. See Licensing for details.
Some countries have a lower threshold of originality and may therefore apply a longer protection term for this image, so it may not be usable in such countries.
To uploader: For this to be applicable, creation year must be known (or known to be at least before 1970)
Dr Jones Edward Salk, creator of Salk polio vaccine, at Copenhagen Airport. During four days stay in Kastrup airport CPH, Copenhagen Dr. Salk paid several visits to the Serum Institute, which was first one outside USA which created a polio vaccine. Dr. Salk also addressed the local Biological Society, 1959-05-28.