NCJ Number
193738
Journal
Journal of Forensic Sciences Volume: 47 Issue: 1 Dated: January 2002 Pages: 178-185
Date Published
2002
Length
8 pages
Annotation
This paper discusses digital rectification processes and resizing methods in order to create life size reproductions of bite mark evidence.
Abstract
Photography is a fundamental tool of forensic science. Bite mark evidence observed in skin injuries or objects is usually photographed for evidentiary documentation, preservation, and analysis. Distortion in forensic evidence photographs reduces the result of analytical procedures available to the forensic odontologist. Inaccurate positioning of the evidence, camera, or measurement reference scale creates perspective and parallax distortion of the captured image. These variables should be eliminated to ensure reliable results derived from comparison of the suspect’s teeth and the bite mark. Detection and measurement of the camera/evidence/scale misalignment is the threshold step in evidence evaluation, and is possible through digital imaging methods coupled with established methods. This study develops type categories of perspective and parallax distortion seen in bite mark evidence, validates the use of digital imaging tools of Adobe Photoshop to correct certain types of distortion, and establishes a forensic protocol to verify the accuracy of evidence photographs requiring dimensional accuracy. According to this study, rectification and resizing of evidence photographs with Type I distortion can be reliably achieved by the examiner using Adobe Photoshop. Type I distortion occurred when the scale within the photograph was on the same plane as the evidence sample; however the camera angle was not perpendicular to that plane. Type II parallax distortion was caused by misalignment of the original evidence and the linear scale, and can be corrected only by re-photographing the evidence sample. By inference, Types III and IV distortion, being subsets of perspective distortion (Type I), were amenable to digital rectification and then digital resizing methods. The results showed that correction of photographic inaccuracies can be achieved within relatively narrow limits. Increased forensic familiarity with Adobe Photoshop capabilities and the digital rectification/resize procedures will lead to better distortion detection and correction. Figures, references