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?