“Whereupon Schwanitz became the inventor of something much more substantial than a 3D Penrose Triangle – he became the inventor of copyright threats over open 3D repositories. A weekend’s worth of acrimony followed – with lots of speculation about the copyrightability of Schwanitz’s design and questions about whether Tchoukanov was guilty of violating any copyright that vested in the design, and further questions about the ethics of copying designs and the ethics of sending copyright threats to Thingiverse.

"Here’s where I net out on it: the 2D Penrose Triangle is not a copyrightable image. It is in the public domain. It is possible to make new copyrighted works based on the public domain (see, for example West Side Story, a new copyrighted work derived from the public domain Romeo and Juliet). The copyrightability of such a work hinges on whether it is sufficiently creative.