Eyewitness accounts are often relied on to solve crimes, but an ISU professor found that composite drawings often don’t share a likeness with their real-life counterparts.

“They’re just pretty bad,” said Gary Wells, distinguished professor of psychology, about composite drawings. “Witnesses look at sets of eyes, noses and chins, and the composite program assembles them into complete faces and the idea is that the police are looking for someone who looks sort of like that. The problem is the real perpetrator rarely looks like the composite.”

Wells said with the development of forensic DNA testing, people who have been convicted of a crime have been found innocent and that eight out of 10 times the wrongful conviction was a case of mistaken identity in a police line-up.

Wells said when people look at faces, they remember the faces as a whole, not individual pieces. The result of picking out individual eyes, noses and chins result in something that looks very little like the actual person.

Wells studied the result of morphing individual composites of the same person and found it looks more like the actual person than the individual composites

in his research paper, “Catching the Bad Guy: Morphing Composite Faces Helps.”

“We tripped across the idea that most crimes have multiple witnesses,” Wells said. “Let’s say we have four people who saw the same crime and each of the four makes a composite face. None of the composites look like the person, but by morphing you are really averaging the face at the level of the pixels.”

Lisa Hasel, graduate student in psychology and Wells’ assistant, said the averaging of faces not only looks more like the person, but the result is a more attractive face as a whole.

“We found that when we did it over and over and over again with different faces, if the actual perpetrator is not attractive, it doesn’t work that well,” Wells said. “It works for all faces but works better for attractive people.”

Hasel said the morphing may actually make the composites more attractive than the people really are, but the overall effect still works. However, if too many composites are used in the morphing, then the person looks like the average person.

“If you morph a number of these composites together, you ultimately create a closer image to the prototypical face,” Wells said in a press release. “So if you put 10 composites together from different people of the same types of face – for example, white males – they would produce a morphed image that would look like the average white male.

“We just went up to four in this study, and it does produce a better likeness of the intended face, although it also does start resembling other faces in that general category. It ultimately would produce more leads, but also a greater chance of including the perpetrator of the crime.”

Wells said he thinks this study is a significant breakthrough in solving crimes and hopes it will be well received by the police department.

A copy of the paper is available through Wells’ Web site at: www.psychology.iastate.edu/FACULTY/gwells/homepage.htm.