Per this discussion, extension of the copyright of works from the Dutch East Indies by the URAA would have considered Indonesian copyright law and not Dutch law. As such, this cover is public domain in all relevant territories.
Copyright for works of: photographic works; portraits; motion pictures; video games; computer programmes; typholographical arrangement of written works; translations, interpretations, alterations, anthologies, databases, adaptations, arrangements, modifications and other work resulting from transformation; translations, adaptations, arrangements, transformations or modifications of traditional cultural expressions; compilation of works or data, either in a machine-readable format or other media, and; compilation of traditional cultural expressions insofar as the compilation is an original work, was expired because it was published more than 50 years ago (Art. 59(1)).
Copyright protection for applied arts was expired because it was published more than 25 years ago (Art. 59(2)).