Movement from film to pixels poses thorny issues

Monday, February 9, 2004

When Victor Reyes went on trial for murder last year, the technology that fingered him was supposed to be a star witness.

Police in Florida had used software known as More Hits to determine that a smudged handprint they had found on duct tape wrapped around a body -- but originally couldn't decipher -- implicated Reyes in the 1996 killing.

The judge let prosecutors introduce More Hits' digital enhancement. But the defense called it "junk science," and had an art professor testify that the process resembled how Adobe Photoshop can be used to make trick-photo illustrations.

Reyes was acquitted.

Jurors said they based their decision mainly on the notion that the print didn't prove Reyes was the killer -- not on the legitimacy of More Hits' method. And a Florida appeals court later ruled that More Hits' technology -- used by 215 U.S. police departments -- is acceptable.

Still, some defense lawyers learned a lesson: Get more aggressive about challenging digitally generated evidence.

"Now whenever you hear the word enhancement, an antenna goes up," said Hilliard Moldof, a Florida defense attorney who is questioning digitally enhanced fingerprints in two cases.

Or in the words of Mary DeFusco, head of training for the Philadelphia public defender's office: "I thought digital was better, but apparently it's not. We're definitely going to take a look at it."

Easier to manipulate

As more police departments abandon chemically processed film in favor of digital photography, the technology could be confounding for the justice system.

Film images are subject to darkroom tricks, but because digital pictures are merely bits of data, manipulating them is much easier.

And although willful evidence manipulation is rare, forensic specialists acknowledge that a poorly trained examiner incorrectly using computer enhancement programs can unwittingly introduce errors.

"What you can do in a darkroom is 2 percent of what Photoshop is capable of doing," said Larry Meyer, former head of photography for State Farm Insurance Co.

Courts have consistently allowed digital photographs and enhancement techniques. But some observers say such methods should endure a more thorough examination, as have technologies such as DNA analysis.

"There have been relatively few challenges to the use of digital technology as evidence and in most of them the courts have looked at them in a fairly superficial way," said Edwin Imwinkelried, an evidence expert at the University of California-Davis law school.

Concerns about the impeachability of digital photographs are one reason many police departments have been hesitant to ditch film for crime scene photographs and forensic analysis.

In fact, some people who train law enforcement agencies in photography estimate that only 25 to 30 percent of U.S. police departments have gone digital -- despite the huge cost benefits of no longer having to buy film and the ease with which digital pictures can be captured and disseminated.

'They're all skeptical'

George Pearl, who runs a civil-case evidence service in Atlanta and is a past president of the Evidence Photographers International Council, sticks with film partly because he doesn't want to explain on a witness stand if he used a computer to adjust the contrast and other settings of a digital image.

"Even if it was honest adjustments," Pearl said. "Juries, they're all skeptical and they're all sitting there waiting to jump on something that's wrong."

Some law enforcement officials also worry about the limitations that still plague digital photography.

Digital pictures can't be blown up as clearly for courtroom displays as well as film photos. Or the compression needed to store a digital file on disk can make the image blurry or blocky, potentially obscuring key details.

"Digital imaging for the most part has a long way to go to meet the quality of film," said Richard Vorder-Bruegge, an FBI forensic expert who chaired a panel that wrote guidelines for law enforcement use of digital imaging.

For example, he said, a negative shot on traditional 200-speed film can produce the equivalent of 18 megapixels of resolution. Only highly specialized, expensive digital cameras approach that now; most that consumers buy are less than 5 megapixels.

Consequently, he believes cops should stay with film for capturing close-up details of footprints and tire tracks.

Many people in law enforcement believe Vorder-Bruegge's assessments are too conservative. They say that with proper training and stringent procedures, digital photos should not be problematic.

In Oregon State Police's forensic laboratory, which has been all digital for about five years, original pictures of fingerprints and other evidence are encrypted so they can't be changed, and burned onto a CD, giving the lab the equivalent of a film negative to reference later.

Any enhancement, such as lightening or darkening elements of the picture -- something traditionally done in film darkrooms as well -- is performed on a copy of the image, not the original, said Mike Heintzman, the lab director.

Erik Berg, a forensic supervisor in Tacoma, Wash., and the developer of More Hits, said digital photos can allow for even more security than traditional means of stowing film negatives in a drawer.

"I have the ability to lock down one or more digital files to a point where I can ensure not only who can or cannot look at it, but for how long, whether or not they can print it or distribute it," he said. "I can also prove whether or not it has been tampered with since it was created."

Perhaps most importantly, software such as More Hits or Adobe Photoshop now can automatically log changes made to an image, so the alterations can be reproduced by other people. The function was not deployed during the Reyes investigation in Florida.

Barbara Heyer, who defended Reyes, concedes that if used properly, the logging function can improve the acceptability of digital evidence.

"Until there's a history of (what was done and when), not only will I attack it, it should be attacked," Heyer said. Otherwise, "you are relying solely on the word of the person doing the work. That's not something I would like to do when someone's facing life in prison or death."

On the Net

More Hits:

Guidelines by Vorder-Bruegge's panel:

Respond to this story

Posting a comment requires free registration: