This paper proposes a technique that can protect the copyrights of digital content for 3D printers. It embeds the information on copyrights inside real objects fabricated with 3D printers by forming a fine structure inside the objects as a watermark. Information on copyrights is included in the content before data are input into the 3D printer. This paper also presents a technique that can non-destructively read out information from inside real objects by using thermography. We conducted experiments where we structured fine cavities inside the objects by disposition, which expressed binary code depending on whether or not the code was at a designated position. The results obtained from the experiments demonstrated that binary code could be read out successfully when we used micro-cavities with a horizontal size of 2 x 2 mm, and character information using ASCCI code could be embedded and read out correctly. These results demonstrated the feasibility of the technique we propose.

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This paper provides a novel technique to embed high-density information in objects fabricated with a 3D printer using a near infrared fluorescent dye. Regions containing a small amount of fluorescent dye are formed inside the object as it is fabricated to embed information inside an object, and these regions form a pattern that expresses certain information. When this object is irradiated with near-infrared rays, they pass through the resin but are partly absorbed by the dye, and it emits near-infrared fluorescence. Therefore, by using a near-infrared camera, the internal pattern can be captured as a high-contrast image, and the embedded information can be nondestructively read out. This paper presents a technique of forming internal patterns at two different depths to double the amount of embedded information. We can know the depth of the patterns from the image because the profile of the brightness of the captured image of the patterns depends on its depth. Using these profiles enables doubling the amount of embedded information. Experiments we conducted demonstrate the feasibility of this technique.

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