When printing 3D objects designed by a particular designer, authentication information such as a serial number and a digital signature of the designer are inserted into a CAD file for printing the object. The authentication information is represented as physical structures in or on the 3D-printed object. The physical structures (e.g., pits, cavities of one or more shapes, etc.) can be detected by a scanner (e.g., an ultrasound or the like), and the detected authentication information can be transmitted to an authentication server that determines the authenticity of the 3D-printed object and transmits the authenticity determination to a user.