Moving from film to digital is like traveling without a road map. Without a clear set of directions, users may encounter more detours than solutions. Taking the plunge to digital involves more than selecting the type of digital camera photographers will use; it also entails determining how images will be processed. To avoid detours along the digital pathway, agencies must consider image authentication and processing software as well as printing equipment.
The savvy agency understands image authentication and knows: what software to use; the differences between image processing and image enhancement; and has looked into processing software long before the first digital image download from the camera to the department PC.
Image authentication is providing proof that the image introduced into evidence is the same image taken at the crime scene. This can be done through testimony of the photographer, other persons present when the photo was taken, and/or through the use of authentication software.
The authentication of digital images is an utmost concern, and how local prosecutors and courts view digital imaging largely determines how authentication will be carried out. With an established record of using digital photos, agencies rarely, if ever, face challenges in introducing digital photos as evidence in court. Prosecutors and courts new to the digital arena may require software authentication until they are comfortable with the images being submitted as evidence. Either way, digital images, as well as 35mm photos should be admissible as long as the following criteria are met:
- Is the image relevant to the case at hand?
- Is the image impartial or not excessively prejudicial to the defendant?
- Does the image accurately represent the scene or item of evidence?
Courts will ultimately answer Questions 1 and 2 if the prosecution and defense attorneys cannot agree on which images to use as evidence. However, Questions 1 and 2 are moot points if Question 3 cannot be satisfied.
For an example of the authentication process, the York County (Virginia) courts have accepted the use of digital images in criminal and civil cases, but the York County/City of Poquoson Sheriff's Office still runs a software-based authentication process as an added measure. This agency relies on a multi-step authentication process for its digital images.
- Once the crime scene photos are taken, the Compact Flash (CF) card is delivered by the photographer to one of three individuals who are authorized to process the images.
- Prior to opening the images, the files are run through a program called HyperHasher and the HashFile tool, both available for download at www.hyperhasher.com. This program takes the image's data, runs an algorithm calculation and creates an alphanumeric 32-digit value for the image file. This file is referred to as an MD5 or Hash value and remains consistent until the image is altered in any way.
- The agency then saves this file as a text document (.txt) to the CF card containing the images.
- The files are burned from the CF card to a CD or DVD, depending on the file sizes.
- Once the CD or DVD is burned, technicians run HashFile again using the images on the CD or DVD, then save this .txt file to the CD.
If the authorized user has Adobe PhotoShop installed, they can perform image authentication through PhotoShop's "Exif Data Reader" available in the File Info menu.
Image processing or image enhancement?
Don't get too hung up on which word to use but be careful how to use them. Webster's defines a process as, "a set of actions," while enhancement is defined as, "to embellish as to improve quality or value." To process a digital image is to perform a set of actions to achieve a desired result. To enhance a digital image is to change its appearance. So, does law enforcement process digital images or enhance them?
With manual or automatic 35mm film, the film is run through a chemical process to develop the negative. With digital media, or in the York County/City of Poquoson Sheriff's Office's case with CF cards, the images are run through a software program to achieve the same results. In 35mm film photography, law enforcement is able to modify the picture size and adjust the color, brightness and contrast through varying levels of exposure. With digital images, photographers use computer software to accomplish similar results. With almost all digital images and any software application for image processing, photographers should limit their processes to size, resolution, color, brightness and contrast adjustments. Enhancement techniques may be used for digital images containing fingerprints or other impression evidence.
Processing or enhancement tools
Processing software is kind of like cars — a person can either opt for the Yugo or the Cadillac. Depending on the size of an agency and the number of crime scene images photographers take, an agency may select one of the mega auto digital processor units such as those found at one-hour processing shops. For small to modest-sized agencies, a stand-alone computer and printer may be all that's required to process images.
There are many software programs well suited to law enforcement digital image processing, but when selecting software, be sure the program has the ability to keep a history log file. The image software most computers come bundled with is often only suitable for image viewing.
Sometimes more than one software tool may be necessary. The York County/City of Poquoson Sheriff's Office, for instance, uses a combination of purchased software and bundled software that came with its cameras and printer.
York County officials use PhotoShop CS for their image processing requirements. PhotoShop is arguably the premier in image processing and enhancement software for digital imaging because there are a number of tools available through PhotoShop that can be used for digital imaging processing as well as video image enhancement. The capabilities of such tools are:
- The ability to add on software programs (plug-ins) that will run through PhotoShop. These individual programs, such as "More Hits Pattern Removal" and "Software and Calibration Utilities," allow users to print images in a 1:1 format — a useful tool for latent fingerprint images. Some of these plug-ins are available as free downloads while some must be purchased.
- The ability to read and process images using the proprietary .RAW image formats of most digital cameras and then convert those images to any number of common image formats. PhotoShop also will read the camera's Meta Data or Exif data to allow users to see what camera and flash settings were used when the image was taken.
- Color inversion, sharpening and gray scale capabilities allow operators to process photographed fingerprint images of fluorescent or white powders on a black background and convert them to black fingerprint images on white. The "un-sharp mask" filter enables users to sharpen fingerprint images that may be slightly out of focus.
- Court display production allows users to chart fingerprint identifications.
While numerous enhancements are possible, the York County/City of Poquoson Sheriff's Office limits its processing to image size, resolution, brightness, contrast and color corrections. Officers are able to use a tool called "curves" to fine-tune image exposure to underexposed images. "Curves" allows equal color adjustment across the full color spectrum.
The York County/City of Poquoson Sheriff's Office sizes its images to 5-by-7-inches (5x7) at a 266 dpi (dots per square inch) resolution. The department selected 266 dpi because it is considered "museum-grade" quality. All of the department's processes are logged in a history file within PhotoShop that can be printed as needed.
The most mundane tasks in PhotoShop can be automated to run automatically. The York County/City of Poquoson Sheriff's Office found this tool particularly useful when officers needed to change the image sizes of approximately 23,000 digital mugshot images for use in a new database.
Most digital cameras will come with a bundled image viewer or software programs. Some have PhotoShop LE (Limited Edition) or PhotoShop Elements, which allow users to perform most processing tasks. However, these programs typically lack the ability to add plug-ins and do not support .RAW camera file formats.
Printing equipment and software
Printers and print software are a dime a dozen. Today even the most inexpensive inkjet printers are capable of full-color, photographic-quality prints. Common issues with some inkjet printers are that the prints may fade over time and may be susceptible to moisture damage. Because of this, a dye sublimation (dye sub) printer is recommended for digital crime scene images. Several models of dye sub printers on the market are in the same price range as mid- to high-grade ink jet printers. A dye sub printer heats the ink onto the paper through several passes and then places a protective coating over the print in the final pass.
The York County/City of Poquoson Sheriff's Office uses an Olympus P-400 and P-440 dye sub printer for its crime scene images. The P-400 has limitations in that it will not print a true 8-by-10-inch image, while the P-440 will.
Kodak also offers several dye sub printers starting in the same price range as the P-440. Through Adobe PhotoShop, York County officials can print to the Olympus printer; they choose to use a program called Photo Record instead, which comes bundled with Canon digital SLR cameras. With Photo Record, officers can import the images and the software will automatically size them as desired, be it 4-by-6-inches (4x6), 5x7, 8-by-10-inches (8x10), a post card, or other customized sizes. The 4x6 and 5x7 sizes allow users to print two images on one sheet of paper. With Photo Record software, users also can print a contact sheet of scene images and optionally include as little or as much of the camera's Exif data such as: the image file name, date, time, camera model, camera serial number and many others.
If an agency's software tools enable the agency to authenticate images as true, create a history of image processes or enhancements, and print photo-quality images that stand up to varying temperatures and humidity levels; it is well on its way to successfully navigating the journey from film to digital crime scene photography.
Troy Lyons is a 17-year veteran with the York County/City of Poquoson Sheriff's Office, where he spent three years in the patrol division before being promoted to the investigations division. He worked as a criminal investigator there for 10 years before being promoted to lieutenant supervising the investigations division. Lyons served as the agency's primary crime scene tech for seven years processing and photographing hundreds of crime scenes with both film and digital SLR cameras. As a state-certified General Law Enforcement Instructor, Lyons regularly teaches crime scene photography and processing.