  Existing approaches for embedding unobtrusive tags inside 3D objects require
either complex fabrication or high-cost imaging equipment. We present
InfraredTags, which are 2D markers and barcodes imperceptible to the naked eye
that can be 3D printed as part of objects, and detected rapidly by low-cost
near-infrared cameras. We achieve this by printing objects from an
infrared-transmitting filament, which infrared cameras can see through, and by
having air gaps inside for the tag's bits, which appear at a different
intensity in the infrared image.
  We built a user interface that facilitates the integration of common tags (QR
codes, ArUco markers) with the object geometry to make them 3D printable as
InfraredTags. We also developed a low-cost infrared imaging module that
augments existing mobile devices and decodes tags using our image processing
pipeline. Our evaluation shows that the tags can be detected with little
near-infrared illumination (0.2lux) and from distances as far as 250cm. We
demonstrate how our method enables various applications, such as object
tracking and embedding metadata for augmented reality and tangible
interactions.
