The development of a tool for assessing the quality of closed circuit camera footage for use in forensic gait analysis

Abstract

Gait analysis from closed circuit camera footage is now commonly used as evidence in criminal trials. The biomechanical analysis of human gait is a well established science in both clinical and laboratory settings. However, closed circuit camera footage is rarely of the quality of that taken in the more controlled clinical and laboratory environments. The less than ideal quality of much of this footage for use in gait analysis is associated with a range of issues, the combination of which can often render the footage unsuitable for use in gait analysis. The aim of this piece of work was to develop a tool for assessing the suitability of closed circuit camera footage for the purpose of forensic gait analysis.A Delphi technique was employed with a small sample of expert forensic gait analysis practitioners, to identify key quality elements of CCTV footage used in legal proceedings. Five elements of the footage were identified and then subdivided into 15 contributing sub-elements, each of which was scored using a 5-point Likert scale. A Microsoft Excel worksheet was developed to calculate automatically an overall score from the fifteen sub-element scores. Five expert witnesses experienced in using CCTV footage for gait analysis then trialled the prototype tool on current case footage. A repeatability study was also undertaken using standardized CCTV footage. The results showed the tool to be a simple and repeatable means of assessing the suitability of closed circuit camera footage for use in forensic gait analysis.The inappropriate use of poor quality footage could lead to challenges to the practice of forensic gait analysis. All parties involved in criminal proceedings must therefore understand the fitness for purpose of any footage used. The development of this tool could offer a method of achieving this goal, and help to assure the continued role of forensic gait analysis as an aid to the identification process.