Discover how to process impression evidence – like tire marks, tool marks, and bite marks – using Amped FIVE. This powerful software enhances, measures, and prepares visual traces for court-admissible analysis. Explore real-world examples that reveal how even subtle impressions can yield critical insights when examined through proper forensic methods and tools.
“Every contact leaves a trace.”
– Edmond Locard
This foundational principle of forensic science goes back to Dr. Edmond Locard (1877-1966), a French scientist who, in 1910, established one of the first forensic laboratories in Lyon. Locard is widely regarded as a pioneer of modern forensic science. Interestingly, his fascination with the field was sparked by the fictional detective Sherlock Holmes. Inspired by Holmes’s methodical use of physical traces to solve crimes, Locard set out to bring those ideas into real-world scientific practice.
He believed that no one can commit an act, especially a criminal one, without leaving behind multiple traces. These traces may either remain at the scene or be unknowingly carried away on the perpetrator’s body or clothing. By the 1930s, this idea had been popularised in North America and was eventually condensed into the now-famous phrase: “Every contact leaves a trace”.
The American criminologist Paul L. Kirk later expanded on this concept by emphasizing that physical traces are objective and persistent. He wrote that wherever a person goes, whatever they touch, step on, or leave behind – be it fingerprints, shoeprints, tire impressions, toolmarks, fibers or fluids – these traces become part of the evidentiary picture. Kirk emphasized that this kind of evidence does not forget, cannot lie, and does not fade. Only our failure to detect or understand it can reduce its value.
He also introduced the Principle of Individuality, the second major pillar of forensic science, which holds that every object is unique. Forensic comparison, therefore, is about linking a questioned trace to a known source. This idea continues to shape forensic work today, including the use of statistical models like Bayesian evaluation to assess the strength of such associations1.
In this article, we will explore how these foundational concepts apply to various types of impression evidence like tire marks, tool marks, bite marks, and indented writing. Each of these can yield valuable forensic information when properly documented and analyzed. Using Amped FIVE, we’ll demonstrate how these traces can be processed, and prepared for meaningful forensic comparison.
Tire Marks
As footwear impressions, tire marks can be individually linked to a specific vehicle and provide important insights into the sequence of events at a scene.
Let’s begin by examining a typical example of a photographically documented tire impression in Amped FIVE.
A look at the histogram reveals that the image is underexposed by about one to two f-stops.
This can be easily corrected using the Exposure filter from the Adjust filter group.
As with all contrast and brightness adjustments, it’s important to monitor the histogram closely during the process. Enabling the “Show Saturated Pixels” option is also highly recommended.
When activated, this function highlights overexposed areas in red and underexposed areas in blue. As long as these saturated regions do not fall within the actual trace, they are not a major concern.
When adjusting the strength of the Exposure filter in the Filter Settings panel, we prefer using the mouse scroll wheel while holding the Ctrl (or Command) key.
This allows for 0.1 increment steps, which enables much more precise control – particularly useful for this filter.
When analyzing tire impressions, it is often not only the length of the impression that matters, but also the width of the tire or specific features within the tread pattern.
In our example image, we only have a scale placed along the length of the tire mark. However, because the image was captured parallel to the ground, this reference still allows us to take additional measurements within the image.
To do this, we can use the Measure 1D filter, found in the Measure filter group.
Within this filter, we first need to define our reference length. To accomplish this, we draw a line as long as possible along the visible scale in the image, which measures 30 cm in this case. We then enter this value into the “Reference Length” field in the Filter Settings panel, specifying centimeters as the unit.
As a quick test, we measured a segment along the scale – from 10 to 14 centimeters – and the filter correctly confirmed the distance as 4 centimeters.
We can now take measurements within the tire impression itself. For instance, determining the width of the tire yields a measurement of 11.37 centimeters.
Tire Marks in Uncontrolled Scenarios
We do not always have ideal conditions when photographing impression evidence.
There may be various reasons for this. For example, the scene circumstances might not allow for a plan-parallel image to be taken. In some instances, the only available material may consist of photos taken by witnesses, or images captured without the awareness they would later require forensic analysis. The following image is one example of such a situation.
The image shows tire impressions, but the scene was neither photographed plan-parallel, nor does it contain a visible scale. However, Amped FIVE still allows us to perform adjustments that enable accurate measurements within the image.
The first step is to correct the perspective. This can be done using the Correct Perspective filter from the Edit filter group.
In this case, we will use the four corners of the manhole cover visible in the image as reference points for the transformation.
A measurement taken at the scene confirmed that the manhole cover is a square with a side length of 80 cm.
Using this information, we can set the correct aspect ratio in the Correct Perspective filter by entering 372 pixels for both the width and height fields.
We can now use the Measure 2D filter from the Measure filter group to enter our measured value of 80 cm for both reference lengths. Additionally, we can draw measurement lines along the edges of the manhole accordingly.
After this, we can take measurements directly on the tire mark.
Just like tire impressions, toolmarks are another form of impression evidence that can offer valuable information in both situational and comparative analysis.
They are created when a hard object, such as a pair of pliers, is pressed or scraped against a softer surface, leaving behind characteristic patterns or deformations.
The following example shows a toolmark left by pliers, enhanced through contrast and brightness adjustments. The gripping surfaces of the jaws have left a distinct pattern on a painted metal surface. This type of trace can help determine the type of tool used and may also be linked to a specific tool recovered from a suspect.
Bite Marks
Another highly important form of impression evidence is the bite mark. Similar to fingerprints, bite marks have the potential to individually identify a person.
Bite marks are most commonly encountered in violent crimes such as assaults or sexual offenses and can be found on both victims and perpetrators. Their evidentiary value lies in the highly distinctive characteristics of dental patterns, which can be compared to dental records or impressions from a suspect.
However, for bite marks – or any impression intended for comparison – to be forensically useful, it is essential to include a proper reference scale in the photograph.
A striking example of this is described in the case study:
“Recapturing a five-month-old bite mark by means of reflective ultraviolet photography”2.
Following a violent rape, law enforcement documented a bite mark on the victim’s skin. However, the photograph taken at the time did not have a reference scale. As a result, by the time the bite mark became critical in the investigation, it held limited evidentiary value.
Only five months later were forensic specialists able to “recapture” the bite mark using reflective ultraviolet photography. This time, they included a proper scale, which ultimately allowed the pattern to be used in court.
This case clearly illustrates a key principle: any photograph of a trace intended for forensic comparison must include a scale. Without a scale, the evidentiary value of the image may be severely compromised, or even lost entirely.
Let’s examine another example of a bite mark in Amped FIVE. This time, we will include contrast and sharpness adjustments, a reference scale in the image and a comparison to the original photograph.
Indented Writing
Another form of impression evidence that plays an important role in criminal investigations is indented writing. This refers to writing impressions left unintentionally on underlying sheets of paper. These impressions can provide critical information in cases involving forged documents, anonymous letters, blackmail notes, or altered records.
There are several well-established methods for detecting indented writing, including:
- Electrostatic Detection Apparatus (ESDA): The most widely known technique, ESDA involves placing the document on a charged surface, applying toner particles, and visualizing pressure-based impressions that are otherwise invisible to the naked eye.
- Oblique lighting: This method uses low-angle lighting to cast shadows across the paper, revealing surface deformations caused by writing pressure.
However, in many cases – especially when working with existing photographic evidence – no oblique lighting was used during image capture. Despite this limitation, Amped FIVE still provides options for enhancing and visualizing indented writing, even when the original image was not taken under optimal conditions.
Let’s now take a look at the following example in Amped FIVE.
At first glance, there appears to be no visible indentations on the paper that would indicate the presence of indented writing.
Let’s apply the Histogram Equalization filter from the Adjust filter group and see what can be revealed.
That already reveals much more information. If we rotate the image 90 degrees counterclockwise using the Rotate filter from the Edit filter group, we can enhance the contrast further. This will allow us to discern even more of the underlying text.
Can you read the full message?
Conclusion
Impression evidence encompasses a wide range of trace types – from tire and footwear marks to tool marks, bite marks, and indented writing.
These traces often result from direct physical contact. When properly documented and processed, it can offer high evidentiary value in both comparative and situational analysis.
As we’ve seen throughout this article, Amped FIVE provides a versatile and effective toolkit for working with these kinds of traces. Whether it’s correcting perspective distortions, calibrating measurements, enhancing fine detail, or visualizing pressure patterns in paper, FIVE provides forensic professionals with a reproducible, structured, and transparent workflow that supports the reliable interpretation of physical evidence.
The key, as always, lies in a combination of good photographic practice, methodical image processing, and an understanding of the underlying forensic principles. When these elements come together, even subtle or initially invisible traces can be revealed and made usable in the context of investigations and court proceedings.
