Digital-Image Management
Written by Kristi Mayo   

digital image management evidence forensic

Useful tips on how to manage your growing digital files

DIGITAL PHOTOGRAPHY in law enforcement has in a very short time moved from a novelty to a potential time-and-money saver to a necessity. “In the future, there will be no such thing as 35mm film photography,” commented Ken Schul of the Charlotte-Mecklenburg (North Carolina) Police Department.

The end of 35mm film photography in the field of law enforcement brings with it some new considerations, some of which may be completely foreign to those who were initiated to film-based photography. Experts agree that any agency that decides to use digital photo-graphy must create a set of standard operating procedures (SOPs), and those SOPs must be followed to the letter.
We spoke with a few experts in law-enforcement photography to find out what practices they find most useful day-to-day when dealing with their digital-image management workflow, as well as some of the common pitfalls that could be encountered when developing your agency’s SOPs.

Tip #1:
Get an archive
and management system

As soon as you put digital cameras in the hands of your officers and investigators, the digital-image files will begin to stack up. So the first thing you need is a good system for moving those images from the camera’s memory card to a computer and subsequently securing, searching, and archiving those images.

“The Charlotte-Mecklenburg Police Department was one of the first large police departments to go totally digital back in 2002,” said Schul, who headed up the agency’s investigation unit when they converted from film to digital. “I learned through the process of that conversion that we needed a lot of different things—but the first and most important thing was definitely an archive and management system. You simply cannot do it without one.”

There are a number of companies that make image-management software that caters directly to the needs of law enforcement. Most of these systems incorporate features that secure the original images and track any changes made to copies of those images in an image editor such as Adobe Photoshop.

There are other developers that offer image-management software to news and commercial photographers, and those systems can also be incorporated into an agency’s SOPs. The drawback is that they may not offer the all-in-one key features—security, tracking, and archiving—that are offered in the law-enforcement management systems.

And as a complete alternative to the more expensive image-management systems, an agency can choose to man-age their digital photos using inexpensive and even free, open-source alternatives—just as long as each step is expressly detailed in the SOPs. It is not as difficult as it may seem, says Erik Berg, a contract latent-print examiner with Harding Security in Charlottesville, Virginia and one of the pioneers who worked for the acceptance of digital photography in the legal community. And it may also help you avoid the pitfall detailed in Tip #2…

Tip #2:
Watch out for
proprietary formatting

“If you choose to use some type of image database, make sure it can be maintained in the event the company goes out of business,” warned Berg. “Many are proprietary systems and store images and data in a way that makes both inaccessible without proprietary software.”

Schul, on the other hand, believes that the benefits derived from a good image-management system designed specifically for the needs of law enforcement override the chance that the images may be unusable should the manufacturer go out of business.

“When you have a sole proprietor, you always have that issue,” said Schul. “But you have to have trust. If something went wrong—for instance, if the vendor failed—there are always other people out there who can come in and assist you to get you up and running.”

Tip #3:
Make sure the images
will stand up in court

There are two things that will help to ensure the integrity of your digital images if and when they are presented in the courtroom. First, you need the strict set of SOPs.

“An SOP that documents the entire workflow is very essential,” said Berg. “SOPs ensure consistency and help avoid difficult questions in court. What you don’t want are individuals who are ‘freelancing,’ doing their own steps and thus exposing the entire workflow to suspicion.”

Second, you need to be able to doc-ument any changes that were made to enhance, clarify, or modify a digital image from its original state. “It is useful to have documentation tools so that when you change something to bring out some important detail in a photo, you can articulate in court how it was done,” said Schul. “Some image-management systems have tools that will do that for you.”

Berg offered another way to prove the authenticity of a digital image. “There are several proprietary methods for establishing whether or not an image has been altered,” said Berg, “but the fastest and most effective methods are based upon a mathematical process known as secure hashing. Hashing generates a unique value for a digital image file. Altering even one pixel in the image will result in a value that is very different from the original.”

There are several different secure-hash algorithms, but one common kind may create potential problems when taken to court, said Berg. “MD5 is the most well-known hashing algorithm, but it has also been broken—meaning that some clever person figured out a way to generate the same MD5 hash for two different files,” Berg explained. “This doesn’t necessarily mean that MD5 can’t be used for law-enforcement purposes, but it does raise the potential for questions. I would stick with the current U.S. government standard: SHA 128, SHA 256, and SHA 512. There are several freeware programs available for generating SHA and MD5 secure hashes.”

Tip #4:
Backup, backup,
and backup again

Anyone who has dealt with computers for any length of time has experienced periodic loss of data—varying from the annoyance of a lost e-mail to the catastrophic failure of an entire hard drive. So it is no surprise that your agency’s image-management SOPs must include provisions for backing up your irreplaceable crime-scene photos multiple times.

There are a variety of ways to back up your images, but here is a brief and straightforward description of how the Charlotte-Mecklenburg PD does it:

First, the original images are burned onto a CD-R, which becomes the “negative” for those images. The CD-R is signed into the agency’s evidence property-control system, and is then signed into the photo lab where it is stored in a special filing cabinet. If the original images are requested in court, the CD-R can be signed out and presented as evidence. Several years’ worth of CDs are maintained in that cabinet; older CDs are handled by an off-site vendor and stored in a controlled area.

Meanwhile, the original images are backed up onto the photo lab’s mini-server as well as the agency’s main server. The main server is backed up onto a tape drive every day and the tapes are taken off-site every 30 days to a controlled location.

In other words: backup, backup, and backup again.

Tip #5:
Don’t be afraid to invest
in storage space

If your agency is just switching from film to digital, take a look at how many pictures officers and investigators were taking with their film cameras in order to determine your future storage needs. According to Berg, people who switch from film-based photography to digital photography take between 5 and 15 percent more pictures.

Or you can consider this estimate: A large department like the Charlotte-Mecklenburg PD—which has about 1,670 sworn officers and about 2,200 employees—takes a total of 450 to 1,000 GB (or about 1 terabyte) worth of digital images every year.

Many agencies choose to maintain their photographs indefinitely. If your agency chooses to back up all of its images on a secure file server (the recommended method for accomplishing long-term storage), that means you will need to periodically increase that server’s storage capacity.

“We just spent about $38,000 to add more storage space,” said Schul, “but that should keep us in business for about six to ten years.”

Tip #6:
Beware of potential issues
with RAW image formats

“A lot of people prefer the RAW image format because it’s the original sensor data,” said Berg, “but the problem with that is that sensor data is not viewable with image-viewing software without some sort of conversion.” That conversion, he said, may not be supported by all software, or the conversion may not be supported by later versions of software in the future. “Nikon and Canon’s formats may be stable,” he added, “but the formats for some of the smaller camera manufacturers may not be so stable in the future.”

Also, bear in mind that RAW image files are large and require more storage space than the JPEG file format.

Tip #7:
Beware of potential issues
with JPEG files

Compressed image formats such as JPEG are useful for saving storage space, but they can also result in an irretrievable loss of image data. There-fore, when using JPEG or some other compressed image formats, Berg says you should use the lowest possible setting to avoid excessive damage to the image quality. “Test against uncompressed image quality so you know what the potential damage is,” he said.

And once you have decided on the image format and compression settings, be sure to document them in your SOPs and make sure photographers strictly adhere to those standards.

Special Media Tips:
Working with CDs and DVDs

Polycarbonate media—in other words, CDs and DVDs—is easily accessible, relatively inexpensive, and tempting to use as a method of backup storage for image files. As with any other decision you will make when establishing your agency’s image-management workflow, however, there are some important points to consider regarding this type of storage media.

CD Tip #1:
CDs do not last forever

“Avoid the use of optical media such as CDs or DVDs for long-term storage,” warned Berg. There are several reasons for this concern. First, National Institute of Standards and Technology (NIST) studies have shown that this kind of media can break down over time, either due to the dyes used by the manufacturers or by inappropriate archival storage conditions. But also, there is the danger that the CD or DVD format could change. “These formats change over time, which could require the transfer of potentially millions of files from the old format to the new format,” said Berg. Consider the recent switch from DVD formats to HD-DVD and Blu-ray (and the relatively quick demise of HD-DVD). “Imagine trying to play music stored on an 8-track tape today,” added Berg.

CD Tip #2:
Don’t use Sharpie
permanent markers to write on CDs

“As we went through our process, we learned that the black Sharpie ink that we used to write on the CDs could possibly leak through the plastic on the CD, hurting the images on the CD,” said Schul.
The danger of Sharpie permanent ink to a CD or DVD is easily solved: just write the case number and other important information on the envelope that holds the CD.

CD Tip #3:
Twin-check the CD

The Charlotte-Mecklenburg PD has an SOP in place that requires the number placed on the CD (using an adhesive label, not a pen—see CD Tip #2) also be printed on the label. This is called twin-checking. “That way, if the CD falls out of the enevelope, we are always able to match up the CD and the envelope again,” said Schul.

CD Tip #4:
Add a slate with information
to each CD

Another method the Charlotte-Mecklenburg PD uses to maintain its images on CDs is to include a text file on each CD that is called a slate. This text file includes the case number or complaint number, the location of the case, the photographer’s name, and the victim’s name. That way, even if the label on the CD is lost and if the CD is separated from its envelope, the image contents can always be identified by popping the CD in a computer and reading the slate.

Digital Photography Tips to Use in the Field

Field Tip #1:
Use a flash to maximize dynamic range

“Digital cameras are getting better all the time, but as a general rule, a digital image is still unable to record the dynamic range of a film like Fuji Reala,” explained Berg. “What this means is that using a flash to take documentary pictures is even more important than it was with film. Flash will help to flatten out the image contrast so that it will fit within the dynamic range of the camera system.”

Field Tip #2:
Reformat your memory cards...regularly

It is important to keep a close eye on your camera’s memory cards because—although they are generally a very stable media—they can be a source of corrupted images. “Check for cracks periodically,” said Berg. “You should also format your cards in the camera, not in a card reader connected to the computer. Formatting will lock out bad sectors.” Be sure to format regularly.

Field Tip #3:
Don’t forget the batteries

Keep your batteries charged and keep more batteries on standby.

Field Tip #4:
Clean your sensors

“A sensor connected to power will actually attract dust,” said Berg. “Every time you remove the lens, the sensor is exposed to the elements. Dust that the sensor attracts will appear as white and black spots on your images.” Clean your sensor regularly according to the camera manufacturer’s recommendations—and avoid changing lenses in dusty and dirty environments. It is also a good practice to turn off your camera before removing the lens.

"Digitial-Image Management," written by Kristi Mayo
September-October 2008 (Volume 6, Number 5)
Evidence Technology Magazine
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