1. A computer-readable medium containing a program which executes the steps of: computing an estimation model using (1) information associated with head-related transfer functions for each of multiple individuals and (2) information associated with physical characteristics for each of the multiple individuals obtained using at least one image of each of the multiple individuals, wherein the estimation model maps physical characteristics of the multiple individuals to audio-related HRTF data for the individuals, respectively; receiving physical characteristics for a subject whose HRTF is unknown using at least one image of the subject whose HRTF is unknown; and processing the received physical characteristics in accordance with the model to produce an estimate of an HRTF for the subject whose HRTF is unknown.