Forensic composite imaging

Whether done by sketch artist or computer, how accurate is it really?

     Whether manual or computerized, composites depend on verbal descriptions that are not always accurate. A basic problem, Wechsler says, is that photofits mostly consist of shape and very little texture. These contours are embellished with scant skin texture, and lack other details that make a person recognizable.

     In addition, researchers find issue with the method in which eyewitness composites are assembled — by individual features.

     Psychological research has shown that people store faces in memory in a holistic way, says Wells, whose research on eyewitness identification is funded by the National Science Foundation. "They don't store individual features but an overall holistic image of the face. And if faces are stored holistically, the best retrieval is holistic," he says. "[Witnesses] don't really have good retrieval access to individual features. Any task to retrieve individual features is going to be profoundly difficult."

     Knowledge of holistic processing may be a boon to future face composite systems that will utilize "whole-face" methods for face recall, according to a February 11, 2007, article in "Science Daily," for which Wells was consulted. Such systems begin by generating a random set of faces. The witness then selects the face most similar to their memory of the perpetrator. This will be the "parent" face that yields a set of similar looking faces, which are the result of several mutations to the parent face. The witness again makes a choice and the process continues until it's impossible to discriminate between the options from his or her memory of the perpetrator.

     EvoFIT software, with British firm ABM as its industrial partner, is one facial composite system based on a holistic face coding scheme and an evolutionary interface. Using this system, witnesses choose from a selection of faces that bear a resemblance to an assailant (a composite is evolved over time by breeding together the selected faces). In recent experiments by Frowd, EvoFIT has outperformed other current composite systems (in the most recent realistic study, EvoFIT reached a level of naming roughly twice that of another United Kingdom composite system).

     Frowd, who has conducted extensive research in the area of facial composites, along with principal investigator Dr. P. Hancock, is currently working on a U.K. government grant at the University of Stirling, Scotland. The aim of the project, called Evolving a Better Composite, reports, is to develop and exploit the holistic (whole face) nature of EvoFIT. There is good evidence that composites produced by EvoFIT are better than other U.K. systems, but research is now required to optimize performance, notes Frowd. Currently, the system generates faces with random characteristics, for a given sex and race, and the user selects those that most resemble the target.

     Researchers wish to make the system more user-friendly by identifying psychologically useful variables, such as age and obesity, and implementing these within the model. This would allow a witness to request that a face be made older, for example, something which requires considerable artistic skill with current facial composite systems, explains Frowd.

     A second aspect of the project is to explore better ways to help witnesses remember relevant details. Current police interviewing techniques concentrate on facial features (e.g. describing the nose), which may work well for today's feature-based composite systems, but gets in the way of remembering what the face as a whole looked like. The researchers' aim is to develop interviewing methods that better match the holistic nature of EvoFIT, and to predict that a combination of these approaches should also enable witnesses with a limited recall (of an assailant) to construct useful composites.

Computerized vs. manual composites
     Frowd et al. also conducted a study titled "An evaluation of U.S. systems for facial composite production" that evaluated the reliability of two systems:

  • San Mateo, California-based Wherify Wireless Inc.'s Faces 3.0, and
  • Scottsdale, Arizona-based Identi-Kit Solutions' Identi-Kit 2000.
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