PROTECTION OF 3D OBJECTS AGAINST ILLEGAL PHOTOGRAPHY USING OPTICAL WATERMARKING TECHNIQUE WITH SPATIALLY MODULATED ILLUMINATION

We present a new technique that protects the copyrights or portrait rights of 3D objects such as sculptures, merchandise, and even human bodies, with optical watermarking, which is produced by spatially modulated illumination. Although the previous study revealed that the optical watermarking technique could prevent objects from being illegally photographed without protection, the technique could only be applied to 2D objects. The largest problem to be solved in extending this technique to the case of 3D objects is to compensate for geometrical distortion. We solved this problem by introducing rectangular mesh fitting and a technique of "bi-linear interpolation" based on the four nearest points. We conducted experiments in which we projected optical watermarking onto the surface of a globe and a model of the human face, and evaluated the accuracy of extracted data. The results were almost 100% in both cases when a Discrete Cosine Transform (DCT) and a Walsh-Hadamard Transform (WHT) were used as methods of embedding watermarks.