FORENSIC IMAGE COMPARISON &
Forensic image comparison or video comparison is the process of comparing known and unknown subjects within digital imagery. We then identify whether an unknown subject matches the known subject. Primeau Forensics offers image comparison, video comparison, and other identification services for criminal defense, law enforcement, and litigators. In addition to these services, we offer a detailed analysis based on case similarities and differences.
THE SCIENTIFIC METHOD: ACEV-R
HOW DOES FORENSIC IMAGE AND VIDEO COMPARISON WORK?
A forensic image and video comparison begins with an assessment between imagery features. This assessment then helps to identify or eliminate subjects. For example, photographic comparisons include:
- A facial comparison between an unknown subject depicted in a surveillance image with an identified suspect.
- The comparison of objects, such as a vehicle, depicted in surveillance images with those recovered in an investigation.
– SWGDE Guidelines for Forensic Image Analysis
QUALITY OF IMAGERY FOR IMAGE COMPARISON
The first step in the investigation is assessing image quality and types of image. In order to accurately interpret the content of an image, it is imperative to recognize the conditions and limitations. These limitations most commonly occur during the time of capture, editing, or image processing. For this reason, digital imagery may require forensic image enhancement in order to view the characteristics for comparison.
IMAGING CONDITIONS THAT CAN AFFECT THE APPEARANCE OF OBJECTS OR SUBJECTS INCLUDE:
IMAGE COMPARISON & Video Comparison CRITERIA
We compare images using practices approved by the scientific community. Criteria for these practices include class characteristics and individual characteristics.
These are identifiable features that narrow the likelihood that a known and unknown object or subject belongs to the same group. However, consistent class characteristics between questioned objects and subjects can only suggest similarities. That being the case, they cannot infer a positive identification on their own.
These are observable characteristics that distinguish objects within a class from one another. They result from random natural and manufacturing processes, intentional alteration, and wear-and-tear. The ability to identify a specific object or subject requires similarity between individual characteristics. With this in mind, analysts determine the sufficiency of these characteristics based on quality, quantity, and persistence of imagery details.
Firstly, a thorough examination of class and individual characteristics between the known and unknown allows an analyst to form an opinion. Secondly, if the objects or subjects in question are the same, the analyst will eliminate all others of the same class.
COMPARISON OF IMAGES FROM VIDEO EVIDENCE
A digital image comparison or video comparison investigation is bound by images of sufficient quality. These images are created by many types of digital camera systems and image formats. Consequently, images must be of sufficient quality to analyze and extract characteristics for the photo forensics analysis.
The most prolific source of police evidence is video images. However, video is not an accurate medium for identification on its own. This is because digital compression removes and adds information that wasn’t originally included. And so, an image forensic expert must be able to interpret the data in order to provide an accurate comparison investigation.
GENERATING AN OPINION
Photographic comparison includes the analysis of imagery, comparison of individual features, evaluation of the comparison’s significance, and comparison verification.
Primeau Forensics utilizes a scale commonly known as the “likelihood scale” or “scale of conclusions.” The scale describes the strength of our opinions coupled with the comparison investigation. Though this confidence scale originated in the United Kingdom, it is now used internationally. Explore the scale in the figure to the right.
EXPERT WITNESS TESTIMONY
As an expert witness, we must present our observations to the trier of fact in a simple, unbiased method. Reports are written from a scientific foundation to ensure that both testimony and reports uphold integrity. And most importantly, all of our opinions are based on scientific analysis rather than subjective reasoning.
Last but not least, we will involve experts from other industries should it help strengthen our investigation. This will, in turn, strengthen our reports and testimony. Follow this link to explore how image comparison and video comparison solved a real case of mistaken identity.