Estimating the Skull-to-Camera Distance from Facial Photographs for Craniofacial Superimposition.

The overlay of a skull and a face image for identification purposes requires similar subject-to-camera distances (SCD) to be used at both photographic sessions so that differences in perspective do not compromise the anatomical comparisons. As the facial photograph is the reference standard, it is crucial to determine its SCD first and apply this value to photography of the skull. So far, such a method for estimating the SCD has been elusive (some say impossible), compromising the technical validity of the superimposition procedure. This paper tests the feasibility of using the palpebral fissure length and a well-established photographic algorithm to accurately estimate the SCD from the facial photograph. Recordings at known SCD across a 1-10 m range (repeated under two test conditions) demonstrate that the newly formulated method works: a mean SCD estimation error of 7% that translates into <1% perspective distortion error between estimated and actual conditions.