Perceptibility of digital watermarking in haptically enabled 3D meshes

Usage of 3D data and models is receiving a growing interest for several applications, like training, museum displays, multimodal interfaces, aid for impaired people. In such a framework the need will soon raise to protect 3D data from misuse. Among the technologies that can be used to this aim, digital watermarking has a prominent role, due to its versatility and non-obtrusiveness. A basic requirement of any watermarking scheme is that the embedded code is invisible, or non-perceivable, by the end user of the data. This requirement also holds for 3D objects, it is then necessary that the human ability of perceiving a signal hidden in a 3D object is studied. In this paper we present a preliminary analysis aiming at comparing the perceptibility of the hidden signal when the 3D model is sensed through different senses, namely vision (through common rendering techniques and subsequent display on a monitor) and touch (through a haptic interface). Specifically our investigation aimed at assessing whether ensuring watermark invisibility is sufficient to ensure that the watermark presence can not be felt haptically. The answer stemming from our preliminary analysis seems to be no, even if further studies are necessary before a definitive answer can be given.