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

Abstract

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.

Forensic odontology in DVI: current practice and recent advances

“…However, images on social media are commonly of low resolution. It takes a great deal of skill to accurately replicate the camera distance and position when securing a PM image for comparison although protocols are available [35], but cadavers are not cooperative. In the case of an AM professional portrait image, the camera may need to be placed as much as 2 m away from the teeth which can be difficult in a mortuary situation.…”

A Preliminary Study of the Reliability of Anatomical Facial Landmarks Used in Facial Comparison

“…Also the image distortion and perspective must be considered when different methodology from the current study will be employed. It is impossible to “achieve an exact alignment” through superimposition due to inconsistency between the reference and comparison images caused by different focal lengths of the lenses, lens distortion, different camera‐to‐subject distances, and various degrees of head‐tilt . These issues will be more critical when measuring different landmarks, not reciprocal ones, employing both 2D and 3D images.…”

“…If any errors occur in positioning of the landmarks, the reference values obtained from the anthropometric analyses are inevitably erroneous . Practically, several factors can influence the precise positioning of the landmarks: the viewpoint of the CCTV camera ; the image distortion due to the object‐to‐camera distance or camera lens ; the image quality ; and operator subjectivity . The viewpoint of the CCTV camera affects the angle of the face.…”

Facial approximation of Tycho Brahe’s partial skull based on estimated data with TIVMI-AFA3D

“…However, even if these factors are controlled, facial superimposition is not considered as a positive identification technique, but a tool used for exclusion [44]. The superimposition of a skull or a FA with Renaissance portraits is moreover complex due to the artistic influence on the facial shape [45,46]. Specific artists, whose technique and style are well documented, may have produced portraits using optical instruments allowing to infer to some extent the resulting distortion, but these cases are scarce [47].…”