Optical ID tags have been shown as a useful tool for surveillance by detection and verification of a signature. Previous work on the topic made ID tags robust to rotations and scale variations by spatially multiplexing the information on the tag. To achieve this goal, however, a large amount of pixels had to be encoded on the final tag. To overcome this drawback an improved design is presented. The information distribution on the ID tag has been modified to optimize the area occupied by the tag. Moreover, a set of reference points has been introduced to achieve resistance against distortions that can affect the tag in remote acquisition. We pay special attention to affine and projective (rotation, scale, shear, perspective) transformations as well as to distortion (barrel, pincushion) caused by the imaging system.
In comparison to prior designs, the novel optical ID tag has two additional advantages: it permits a significant reduction of the tag size, even if the verification is remote and affected by the aforementioned distortions. Verification results are presented for a number of practical situations.