In a distributed or multi-user system, it is possible for a user to try to access a media file that is not optimal for the user’s purposes. The scanning unit includes a scanning plate having a splitter that splits the beam of light into a measurement beam and a reference beam, wherein the reference beam is propagated solely within the scanning plate before reaching interferential superposition with the measurement beam at a unification site. A selected challenge is then communicated between the input device subsystem and the host. Each interior recycle can insert tapers from the top periphery to the lower periphery to facilitate easy insertion and removal from the outer receptacle.