Digital Evidence Raises Questions


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.

But the defense had an art professor testify that the process resembled how Adobe Photoshop can be used to make trick photo illustrations.


Hector Hernandez of the Oregon State Police examines a digital image
of a fingerprint on a pop can in a lab in Salem. Critics note it's easier to
manipulate digital images than film
. (Don Ray/Associated Press)


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 attorneys 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.
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, 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.

The police department in Santa Clara, Calif., bought 30 digital cameras recently but is holding off on giving them to detectives and technicians until the department specifies ways to lock away the original photos as evidence “so there can be no question that anything was changed,” said Sharon Hoehn, an analyst for the department.

George Pearl, who runs an evidence service for civil cases 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 worry about the limitations that still plague digital photography.
Digital pictures can’t be blown up as clearly for courtroom displays as film photos can. 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.