Forensic composite imaging

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

     Law enforcement has used facial compositing to help solve crimes since Billy the Kid was a fugitive in the American Wild West.

     Conventionally, sketch artists created hand-drawn renderings with charcoal or pencil. But today the use of sketch artists is becoming increasingly rare in criminal investigations, often reserved for only the largest departments. The sketch artists of old are quickly being replaced by facial composite software.

     While the work of artists is being taken over by computerized tools, the functions of forensic composite imagery have expanded. It is used for identification of persons or objects, image modification, depictions of crime scenes, and reconstruction and post mortem identifications, says James Lucas, adjunct faculty at Oakton Community College of Illinois.

     But some experts are questioning the accuracy of these tools — and of composites or photofits in general.

     In an article appearing in the February issue of "Current Directions in Psychological Science," Gary Wells, professor of psychology at Iowa State University whose studies of eyewitness memory are widely known and cited, and co-author Lisa Hasels, also from Iowa State University, point to several studies that indicate facial composite systems produce a poor likeness of the intended face. According to the article, researchers had inferior results in studies where individuals attempted to create composites of famous celebrities. In one study, just 2.8 percent of participants correctly named the likeness of a well-known celebrity created with face composite software.

     Researchers like Wells are concerned because of the potentially negative consequences of a bad composite. Broadly distributed to law enforcement, newspapers and the public, an inexact image may lead an investigation astray and produce wrongful convictions. A sketch of the Unabomber in a hood and sunglasses created a virtually useless rendition of Ted Kaczynski, and he eluded law enforcement for many years. On the other hand, strong links tied Timothy McVeigh to the Oklahoma City bombing, among them the fact that his appearance matched eyewitness accounts used by FBI artist Raymond Rozycki to develop a composite drawing.

     "There is a presumption — if we have a tool use it. But [what we're saying is] wait a minute, be careful here," Wells cautions.

Flaws in thefacial composite process
     Dr. Harry Wechsler, a noted expert on biometrics and face recognition, who serves as professor of computer science and director of the Center for Distributed and Intelligent Computation at George Mason University in Fairfax, Virginia, points to articles by G. Daniel Lassiter published in "Current Directions in Psychological Science" (2002) and Dr. Charlie Frowd, a researcher at University of Central Lancashire, whose primary research involves improving the quality of facial composites, in "Psychology Crime and Law" (2005).

     Frowd's article titled "Contemporary composite techniques: The impact of a forensically relevant target delay" outlines the lackluster performance of composite naming using a two-day delay between the time a witness saw the perpetrator and when he or she worked with the forensic artist. His study concludes that composite naming, that is, identifying a subject by matching a composite against a database, though a photo lineup or a police bulletin, "was surprisingly low," says Wechsler. In fact, composite naming was successful in only 3- to 8-percent of the studied cases.

     Yet facial composite software may not be to blame, Wechsler says. Numerous factors affect the accuracy of eyewitness composites: A delay following the event, exposure time to the subject, target distinctiveness, emotion, stress, all play an important role in the composite produced.

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