THERE’S GOOD NEWS AND BAD NEWS: LOWER PROCESSING COSTS AND DIMINISHING
FILM AVAILABILITY HAVE DRIVEN FORENSIC SCIENCE TOWARD DIGITAL PHOTOGRAPHY.
Last summer, Reuters admitted that two digital photographs presented as part
of its coverage of the 2006 Israel-Lebanon conflict had been significantly
altered before being published. One photo showed two heavy columns of black
smoke billowing from Beirut buildings after an Israeli air attack. Another
showed an Israeli aircraft supposedly firing several missiles.
The images were withdrawn after manipulation was exposed by a U.S. blogger
(LittleGreenFootballs.com), who accused Reuters of distorting the first photograph
to include more smoke and damage than actually existed. In the other, an Israeli
Air Force F16 that had deployed a single flare was digitally doctored to make
it appear that several missiles had been fired. Reuters subsequently admitted
that the photographer had altered the images using photo-editing software.
The incident illustrates the principle issue with the use of digital photography
in forensics, especially in fields like news gathering and criminal justice
where the pressures of ethics and public trust are pervasive and presumably
paramount.
“Manipulation of digital photographs is not only quite possible,
but quite easy,” said Howard Adelman, M.D., a New York forensic pathologist. “With
digital photography, I always try to imprint the date and time on the photo
and, especially with specimens and bodies, have a ruler in the picture.”
Alteration
of digital photographs is far simpler than traditional film. Almost anyone
with just a little practice with basic imaging software can produce changes
that are nearly impossible to detect without special steps. A person can
remove a blemish or a scar from a portrait, a scratch or dent on a car in a
newspaper
add, or change a license plate, the time on a clock, or background objects
in a crime scene photo.
PICTURE OF STEALTH
The potential for image manipulation provides a basis for broad admissibility
challenges in court. The judiciary has had to increase its scrutiny to be
assured digital evidence is authentic and has not been altered or ‘Photo-shopped.’ There
have always been legal issues associated with the introduction of photographic
evidence, but the digitalization of photographs presents new challenges to
forensic scientists to track and maintain image integrity.
“The ease
with which images can be manipulated heightens the need for proper authentication,” said
Florida attorney Catherine M. Guthrie, a staff researcher at the National
Clearinghouse for Science, Technology, and the Law at Stetson University
College of Law. Guthrie is co-author of an upcoming law review article titled “The
Authentication of Digital Images: The Swinton Six.”
Authentication essentially means that evidence, in this case digital images,
are in fact what they purport to be. In other words, the pictures and the processes
used to generate them are accurate and reliable, Guthrie said.
Los Angeles attorney Darren Enenstein said one way to authenticate digital
images is by using hash functions, or algorithms that give a mathematical
formula (or
hash value) to each image.
“You can then compare the photo’s hash
value if it is moved or copied. If the hash value matches then it is the exact
same image, with no changes,” Enenstein said. Enenstein cautioned that
algorithms used to compress images for storage can change a hash value.
Software
packages, such as Adobe Photoshop CS, are available that produce change reports
for digital photo files. Camera manufacturers are also sensitive to the image
integrity issue. Several years ago Olympus released its Image Authentication
System that can be used to verify if an image has been altered. Canon currently
has a Data Verification Kit for its EOS 1Ds and EOS-1D mark II cameras that
can detect changes as small as one bit.
“Case law supports the use of these
tools,” said Robyn Diehl Lacks, an assistant professor of law in the Wolder
School of Government and Public Affairs, Virginia Commonwealth University.
Some camera manufacturers now offer a read-only raw file format. The benefit
of raw files is that they are virtually unalterable, an advantage for archival
purposes. There is a problem with this format, however. According to a 2004
Adobe White Paper titled “Digital Image Integrity,” written by
George Reis, Imaging Forensics (Fountain Valley, California), when a raw file
is opened, the
raw data is read from disk and processed into a file that can be viewed on
a monitor, which completely transforms the file from raw state.
“The
data cannot then be re-saved in a raw format,” the paper states. “The
processing information used when a raw file is opened cannot ever become part
of the original archive file. So, although the raw file largely retains its
integrity as an unaltered file, it doesn’t include processing information
that is frequently crucial to forensics.”
PICTURE PERFECT
In general, courts have held that the proponent of the evidence needs to prove
that either the proffered photograph is an unedited original or, if editing or
enhancement was involved, that the changes were made on a copy of the original,
with the original being preserved, and every step in the process was recorded
such that each step could be repeated if necessary.
Challenges to digital evidence rarely occur in court, however. Jill Witkowski,
writing in Can Juries Really Believe What They See? New Foundational Requirements
for the Authentication of Digital Images (10 Wash.U.J.L. & Pol’Y 267,273(2002))
says a possible explanation for this is the legal community’s general lack
of awareness of the characteristics of digital images that could make them less
reliable than traditional film as evidence.
“Because of the few challenges
and therefore scarcity of case law on the subject, the lack of awareness of the
unique evidentiary issues digital images present is perpetuated,” Witkowski
said.
One 2004 case (Connecticut v. Swinton) involving challenges to digital photographic
evidence did wind its way to the Connecticut Supreme Court. In Swinton, the
defendant challenged the admissibility of two digitally enhanced submissions – photographs
of a bite-mark on the victim’s body and images of the defendant’s
teeth superimposed on the bite mark.
Case law established in Swinton provides guidance in how to lay proper foundation
when submitting digitally produced evidence. There must be testimony by a person
with some degree of computer expertise, who has sufficient knowledge to be
examined and cross-examined about the software and its operation. Further,
beyond the
reliability of the evidence itself, the proponent must establish:
the
equipment used is accepted as standard equipment in the field;
the
operator of the equipment was qualified to use the equipment;
that
proper procedures were followed in connection with the input and output
of information; and
the
software used is reliable.
Federal Rules do not currently set forth admissibility requirements for digital
photographs (McCormick on Evidence, 214 (5th Ed.,2003 Pocket Part), so traditional
notions of relevancy and authentication apply.
FINISHING TOUCH
The forensic community is well aware that concerns regarding manipulation of
digital images are just as crucial as they were with film.
“Digital
photography has not only penetrated the forensic front, it has become incumbent
upon the forensic sciences to embrace applications if the current state of
the science is to be achieved,” said Gregory S. Golden, chief odontologist
for the County of San Bernardino, California.
Organizations such as SWGIT (Scientific Working Group on Imaging Technology)
are responsible for setting down protocol and guidelines for digital imaging
applications.
SWGIT has worked for a decade to help criminal justice transition from a film-based
to a digital-based society. One of its documents, “Recommendations and
Guidelines for use of Digital Image Processing in the Criminal Justice System,” helps
ensure that processed images can be successfully introduced in court.
“Legal
challenges have mostly been concerned with processed images,” said SWGIT
chair Carl Kriigel. SWGIT’s position is that any changes to an image
made through digital image processing are acceptable in forensic applications
provided the following criteria are met: • The original image is preserved; • The
processing steps are logged when they include techniques other than those used
in a traditional photographic darkroom; and • The end result is presented
as an enhanced image, which may be reproduced by applying the logged steps
to the original image.
SWGIT has produced several other documents, including guides for management
(“Considerations for Managers Migrating to Digital Image Technology”)
and training (“Recommendations and Guidelines for Training in Imaging
Technologies”).
“The consistent and reliable use of video and digital
imaging technologies in the criminal justice system requires competent and
appropriate training of personnel,” Kriigel said. All 15 of SWGIT’s
documents are available online at the International Association for Identification
website (www.theiai.org).
The American Board of Forensic Odontology has adopted similar guidelines
for image management (www.abfo.org).
BIG PICTURE
Digital imaging began penetrating the criminal justice community about 15 years
ago; although at that time only low resolution digital cameras were affordable.
“Some
agencies attempted to replace all their film cameras only to be disappointed
with the quality digital gave them,” Kriigel said. “Some of these
same agencies re-thought their procedures and have kept film cameras until
the resolution of digital cameras began to approach film resolution.”
During
this transition, many agencies opted for a hybrid system wherein film cameras
were used for identification photography and digital cameras for recognition
photography, Kriigel said.
With increased resolution of digital technology and cost of high-end digital
cameras dropping to affordable levels, digital photography is now replacing
film in those agencies anxious to eliminate toxic chemical developing systems,
opting instead for computers, monitors, and printers.
“Processing film
has become a thing of the past,” Kriigel said. “Many agencies find
they actually have more digital cameras being used than they ever had film
cameras.”
Herbert Blitzer, executive director of the Institute for Forensic
Imaging at Indiana University-Purdue University at Indianapolis said, “Everybody
is going digital, because you can save a lot of time and money if you don’t
have to process film and make paper prints.” Another reason, Blitzer said,
is film is going away. Kodak, for instance, stopped making black-and-white paper
in 2005.
“Specialized film in particular is hard to find anymore,” Blitzer
said. Even when special film can be found, processing times have become impractical.
Cincinnati odontologist Franklin Wright said it can take up to two weeks to
get black-and-white infrared images back from the lab. “By then, if you have
a deceased victim, there is no bite mark to re-photograph, if necessary, and
if the victim is living the wound has healed,” he said.
Digital photography offers other advantages over film.
“Immediate viewing
of images via LCD minimizes errors and the need to re-shoot subjects or scenes,” Golden
said.
The ability to store, transfer, and reproduce images electronically from
anywhere to any other location in the world within minutes, with no loss
of resolution,
presents another unique advantage to forensic investigation.
SHOT IN THE DARK
One issue forensic photographers had with digital imaging was recently addressed.
As digital photography penetrated deeper into the forensic world, there was
concern among forensic specialists that digital technology would leave a
capacity vacuum. Golden, Wright, Robert Chessman of RC Forensics in California,
and others began pleading with digital camera manufacturers to provide a
digital camera with at least the same capabilities that existed with traditional
film cameras.
“Business models of most digital manufacturers is to
sell large quantities of cameras at a small profit,” Wright said. “They
weren’t concerned with forensic applications.”
At least one manufacturer
heard the demands. In August, Fujifilm broke new ground with the introduction
of its FinePix S3 Pro UVIR camera, the world’s first production D-SLR
(digital single lens reflex) camera capable of taking photographs in the
ultraviolet and infrared light spectrums. [See related article on page 22]
The UVIR camera was designed specifically for use in science, medicine, forensics,
and fine arts. Law enforcement agencies have used special ultraviolet and
infrared photography for years to uncover evidence difficult if not impossible
to see with the human eye, such as gun shot residue and blood stains, as
well as to recover altered, burned, or obliterated writing.
The Fuji camera is the first DSLR to feature a live CCD previewing feature,
a significant aid to the forensic photographer because it enables manual focusing
while dark filters are attached to the lens, as well as precapture verification.
Some beta testers of the UVIR camera, however, have noticed that the digital
UV images look different than images taken with traditional panchromatic films.
“That
may be because the film has a wider latitude at the low end of the spectrum,
or the chip is picking up something other than pure UV,” Golden said.
Golden intends to determine what level of the spectrum is transmitted through
the two different filters used for each application, UV and IR.
“My hunch
is that some IR is passing through the 18A UV filter,” he said, “however
this needs to be confirmed with a spectrophotometer.”
WHO’S MINDING THE STORAGE?
There are other issues inherent in digital
photography.
While digital offers substantial cost savings over traditional
film processing, you still have to
store those digital images. That means agencies can end up with large, fragile
libraries stored on electronic media that is subject to obsolescence.
“Storing
all those photographs can be a huge issue,” Blitzer said. “You
can’t just save images on a hard drive and expect them to be there forever.”
Courts
require that trial documents be kept for decades. Indiana forensic photographers,
for instance, shoot 400,000 to 500,000 pictures a year, and Indiana court rules
specify that evidence must be kept 55 years.
“That’s a lot of data
to archive for half a century,” Blitzer said.
Compression is one solution, but it comes with its own downside. Compression
refers to processes that reduce the size of image data files, which tend to
be quite large, so that less storage space is required. The two techniques
used for this form of alteration are lossless and lossy compression.
Lossless compression reduces the file size by removing redundant data. Because
the redundant data can be retrieved during reconstruction of the image for
display, lossless compression results in no loss of information. An example
of a file format that uses lossless compression is the graphical interchange
format (GIF).
Lossy compression, such as JPEG (Joint Photographic Experts Group) achieves
even greater reduction in file size by removing both redundant and irrelevant
information. Because the irrelevant information (as determined by the compression
algorithm), cannot be retrieved during reconstruction, this method not only
results in some loss of image content but can add artifacts, rendering the
images less useful forensically. The higher the compression ratio, the greater
the data loss.
“Compression is considered a form of alteration, and any
alteration may arguably distort the accuracy of the image,” Guthrie
said.
Most legal experts agree that the ‘best evidence’ rule should
apply when offering digital photographs as evidence, and that the original ‘best
evidence’ version of a digital photo is the disk drive in the camera
itself, prior to being downloaded to a computer.
Douglas Page writes about forensic science and medicine from Pine Mountain,
California. He can be reached at douglaspage@earthlink.net
