Forensic composite imaging

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


     The study, which is to be published later in 2007 in "Ergonomics" is posted on www.uclan.ac.uk/psychology/research/people/Frowd.html.

     In this study, Frowd states researchers found U.K. software programs produce composites that are correctly named about 20 percent of the time when participant-witnesses attempt construction either immediately or a few hours after seeing a target face. Unfortunately, he says, when participant-witnesses are required to wait two days before they can construct the composite — a situation typical of real police witnesses — composite naming fell to a few percent correct at best, according to statistics gathered in research for journal articles "The Process of Facial Composite Production" in "Forensic Psychology and Law" and "Parallel Approaches to Composite Production" in "Ergonomics."

     A comparison of three U.K. programs, a sketch artist and Faces 3.0 (a program not differing so much from later version 4.0 that results are invalid) were the subject of another Frowd study. It found that composites done by a sketch artist were correctly named 8 percent of the time, but the other systems were worse — naming was less than 4 percent.

     A 2005 study by Frowd et al. comparing computerized systems with manual systems found that all other composite systems tested were inferior to a sketch artist. While it may be that the skill of the person was responsible for this, he says the mode of representation might be as well. It turns out that sketch artists working with witnesses tend to produce composites with less shading compared with systems, such as ABM's PRO-fit and FACES, which utilize photographed features, especially in areas around the forehead, cheeks, nose and chin. It might be that these features, Frowd notes, are better left blank rather than including potentially misleading shading information. As such, sketched composites may contain less incorrect information and may be more identifiable.

More research needed
     More research is definitely called for. Anecdotal evidence touting the successes of composite sketches can be dangerous. "It's in the nature of anecdotes to be selective and to ignore all cases where it didn't work," says Wells. "Our approach has been to drop the anecdotes — we like to study in controlled conditions … we know which face [witnesses] saw and how well they do in generating the face. Software has improved incredibly but there's still a problem in getting likenesses. The [issue] doesn't seem to be within the software itself."

     Wells calls Frowd's research "promising," and continues to hope for more controlled studies and police software programs that stand up to scientific criteria. "If we can't make them better," he says, "we should use them less or as a last resort."

     On the other hand, taken with other evidence, composites can assist investigators. "Photofits factor out many biometric features," says Wechsler, "narrowing down the police work to identify suspects and thus making [their job] easier and more efficient." Efficiency increases because investigators narrow the subset of suspects, and accuracy improves because they can spend more time on a reduced set of suspects.

     Perhaps Lee Farrow, FACES global account manager at Wherify Wireless Inc., says it best: If we compare finding a suspect through use of facial composites to finding a needle in a haystack, "facial composites may make the haystack a little smaller or the needle a little shinier."

     She continues it's critical to remember that a facial composite gives investigators "a direction but it's not the nail in a coffin — there's additional evidence like DNA or fingerprints." It narrows down the suspect, but "it's not the finalized tool to arrest someone."

Donna Rogers is a freelance writer based in Huntington, New York. She can be reached at drogerskranich@verizon.net.

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