Three-dimensional (3-D) printing has become a key technology, changing industry paradigms in many sectors, including automobiles, aerospace, medical applications, content production, and service areas. However, 3-D printing introduces many copyright infringement issues for digital 3-D objects because the object data can be directly printed and distributed both online and physically. New distribution scenarios not previously considered also pose new content security problems. This paper reviews intellectual property protection issues and solutions in the 3-D printing environment. We summarize various requirements not previously considered in the literature, defining infringement issues for new technology scenarios and requirements. We then analyze existing copyright security technology coverage according to those scenarios and various other aspects, and present the pros and cons of each technology and future research directions. The presented scenarios and reviews will provide significant benefits for the future development of reliable technologies that protect the 3-D printing intellectual property.