We present an experimental color image encryption by using a photorefractive crystal and a joint transform correlator (JTC) architecture. We achieve the color storing by changing the illumination wavelength. One JTC aperture has the input image information corresponding to a determined color channel bonded to a random phase mask (object aperture), and the other JTC aperture contains the key code mask. The joint power spectrum is stored in a photorefractive crystal. Each color data is stored as a modulation of birefringence in this photosensitive medium. The adequate wavelength change produces a corresponding power spectrum modification that avoids image encryption cross talk in the read out step. An analysis in terms of the sensitivity of the photorefractive silenite crystal for different recording wavelengths is carried out. It should be highlighted that the multiplexed power spectrum shows neither the multiplexing operation nor the amount of stored information increasing the system security. We present experimental results that support our approach

Abstract. Optical ID tags have been introduced and described to achieve remote target recognition and identification. Optical ID tags usually contain encrypted signatures to be read out, decrypted and verified. In this paper, new features are introduced so that ID

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.