Discover how forensic fingerprint analysis reaches new levels of clarity and precision with Amped FIVE. This article explores advanced techniques for enhancing, preserving, and presenting fingerprint evidence, even in complex cases involving difficult surfaces or lighting conditions.
“The little things are infinitely the most important.”
– Sherlock Holmes, A Case of Identity (Arthur Conan Doyle)
When it comes to determining a person’s identity, fingerprints are certainly among the first of these “little things” to be mentioned. Even over 4,000 years ago, people were aware of the uniqueness of fingerprints. The Assyrians and Babylonians, for instance, would imprint their clay tablets – used as official documents – with the name of the author and with their fingerprints pressed into the clay to confirm authorship.
As early as 1160, the Chinese writer Shi Nai’an described in his crime novel The Water Margin how murder suspects were required to ink their fingers and leave prints. In Europe, however, the significance of fingerprints in criminal proceedings was not recognized until much later, during the 19th century.
Fingerprints, however, are not only of great importance in identifying suspects. They can also play a crucial role in the identification of bodies, particularly when other methods fail. This is especially important in cases where the body is badly damaged, such as after a fire.
On the Significance of Fingerprints in Criminal Proceedings
The importance of fingerprints in criminal investigations and court proceedings is unparalleled. The dactyloscopic trace remains the only type of evidence that allows for the unequivocal identification of the individual who left it. Its evidentiary value even surpasses that of DNA analysis. Thus, its significance cannot be overstated.
(Biologische Spurenkunde, Vol. 1: Kriminalbiologie, Bernd Herrmann, Klaus-Steffen Saternus, Springer 2007)
This assessment is based on the uniqueness and permanence of the skin ridges that form fingerprints. The term dactyloscopy derives from the Greek words dactylos (finger) and skopein (to look), meaning “finger examination”.
Due to the central importance of dactyloscopic traces, particularly high standards are required for their preservation.
The following brief overview outlines the steps necessary for preserving fingerprint evidence, highlighting the level of care and precision needed. The aim is to raise awareness that these high standards must also apply to all digital preservation and processing stages.
The Importance of Photography for Forensic Fingerprint Acquisition and Analysis
This overview focuses specifically on photography’s role in preserving dactyloscopic evidence. Photography is one of the most important – if not the most important – methods for securing fingerprints, and it is invariably linked to subsequent image processing. Even when a fingerprint is initially made visible through chemical or physical methods, it still requires further photographic documentation or enhancement. This step is necessary to visually separate the fingerprint from the background or substrate.
Since some detection methods reveal fingerprints only temporarily, permanent preservation via photography is essential. Furthermore, the photograph must be converted into a specific format for comparison with reference prints. In most cases, photographic documentation provides the highest quality and avoids the risk of damaging or degrading the evidence.
Visual inspection is the first step in examining any evidence that may contain dactyloscopic traces.
In combination with photography, it serves as an exploratory procedure that can reveal the location and distribution of fingerprints. Beyond securing fingerprints, this step also provides crucial information for planning the next steps in the investigation. It is particularly important to avoid trace overlap or contamination, such as with DNA evidence.
Understanding certain principles of forensic fingerprint photography is beneficial for some of the processing steps later performed in Amped FIVE.
As with video editing, fingerprint editing in FIVE can be divided into two categories:
- restoration
- enhancement
Just like with video footage, it is essential to understand which factors are critical for achieving optimal quality when photographing fingerprints. It is equally important to recognize the points in the image creation process where quality can be negatively affected.
Characteristics of an Image with Optimum Quality
- It is absolutely correctly focused and motion blur-free.
- It was taken with the basic sensitivity of the camera sensor, which means that the image has the lowest noise and the highest possible dynamic range.
- It reproduces colors and tonal values correctly.
- It is taken with the so-called favorable aperture. Each lens has a specific aperture value that produces the sharpest image.
- It is free from optical errors and free from perspective distortion.
These characteristics, as mentioned, are general and apply to all types of photography. In forensic or crime scene photography, however, several additional requirements and modifications are added to these general principles.
Forensic photography focuses specifically on the region of interest, particularly when capturing accurate tonal values. For example, it may be necessary for large areas of the image to be overexposed or underexposed. However, the trace itself – whether it’s a fingerprint, shoeprint, or piece of evidence – should be optimally exposed in terms of tonal range.
In addition, there are three so-called cardinal rules of forensic photography:
- Maximum Depth of Field: This means that all parts of the region of interest must be sharply focused, even if they lie on different spatial planes.
- Frame-Filling Composition: The region of interest should occupy as much of the sensor area as possible to ensure the highest possible resolution and detail.
- Planar (Parallel) Image Capture: The camera should be positioned parallel to the surface being photographed. This avoids perspective distortion, supports rule #1 by maximizing the depth of field, and ensures the region of interest is reproduced accurately.
As with the general characteristics of a high-quality image discussed earlier, we will see later in this article that there is no rule without exceptions.
Before we begin exploring how fingerprints are processed in FIVE, let us first review some of the fundamental principles involved in fingerprint image editing.
Basic Components of the Digital Processing of Fingerprints
After any fingerprint preservation process, the secured fingermark must be evaluated by an expert and compared with a reference print from a suspect.
As previously mentioned, the preserved mark must be presented in a specific format to allow for proper comparison. This includes, among other things, ensuring that the fingerprint appears dark against a light background with the highest possible contrast.
Below is an overview of the essential steps involved in digital image processing of fingerprints:
- Contrast Optimization Relative to the Background
This process typically involves adjusting the tonal values of the image. It can be done through tonal value correction or modification of the gradation curve. It may also be necessary to suppress distracting features of the background, such as colored patterns, by adjusting individual color channels. - Conversion to Greyscale
If the fingerprint image has not already been rendered monochrome through earlier processing steps, it should be converted to greyscale. This is also necessary if the original trace was already monochrome. - Optional Image Inversion
In some cases, inversion may be required, such as with fingerprints developed using cyanoacrylate vapor. These often appear light against a dark background. Sometimes, it is not immediately clear whether an inversion is needed for the entire image or just specific areas of the fingerprint. - 1:1 Calibration
The image dimensions must be calibrated so that any subsequent printout of the fingerprint is reproduced at the exact same scale as the original trace. This is critical for accurate comparison and identification.
So, let’s get started by taking a look at a basic analysis workflow in FIVE.
As an example, we will examine a fingerprint that has been visualized using one of the most common development methods: cyanoacrylate fuming, also known as super glue fuming.
For all non-porous surfaces, this is perhaps the most widely used technique for developing latent fingerprints in high quality. It is a well-established method that provides strong contrast and good stability, making it an ideal basis for further digital processing in FIVE.
Simple Basic Forensic Fingerprint Analysis Workflow
The first step – after opening the image – is to activate both the histogram and the overexposure warning. These tools allow you to monitor in real-time whether any adjustments during the editing process have resulted in overexposed or underexposed areas within the fingerprint.
From this point onward, whenever we refer to overexposed or underexposed areas, we will also use the term saturated pixels. This refers to image areas where the sensor data has reached its maximum or minimum limit. Therefore, these areas no longer contain usable tonal information, which we must avoid within the region of interest.
A few basic principles must be kept in mind when processing fingerprint images.
Any modifications made to the image file must be fully documented and reproducible. It must be ensured that all results obtained during processing are repeatable and comprehensible.
Furthermore, all edits and enhancements must be communicated to the expert responsible for evaluating the fingerprint and comparing it to a reference print. The results must be provided in a format that clearly shows every adjustment made. This allows the entire process to be transparent and easy to follow.
Similar to handling video files, all of this can be efficiently managed in FIVE by generating a report. In addition to the report, FIVE’s bookmark feature allows users to insert comments at key points in the workflow. This makes it easy to annotate and explain specific steps.
Such comments might look like this:
With that in mind, let’s return to our fingerprint analysis workflow and continue with the next steps.
If necessary, you can now adjust the orientation of the image using the Rotate filter.
By examining the histogram, we can determine that the image is underexposed by approximately one to two f-stops. This indicates that the overall brightness is too low. Important details – especially in the darker areas – may not be fully visible or usable for further analysis.
We can easily correct this by using the Exposure filter, for example.
When adjusting the tonal values, we now see that FIVE gives us a warning. It highlights the areas in red where overexposure begins to occur – that is, where the pixels become saturated.
In general photography, this is something we typically try to avoid. However, in our case, it is not a problem – as long as the saturation does not occur within our region of interest.
Inverting the Image (Negative)
In principle, the fingerprint should appear dark on a light-colored background. However, depending on the trace development method and lighting conditions, the fingerprint may instead appear light against a darker background.
In such cases, the fingerprint must be inverted. This can be done globally by applying the Negative filter to the entire image.
However, it is also possible to invert only the region of interest. For this, we can use the Curve filter from the Adjust category. This filter can be applied selectively to a specific area only.
Next, then return to the Value tab, which displays the curve. The two points at the bottom left and top right of the curve are important here.
Move the bottom left point all the way to the top left and the point at the top right is moved to the bottom right.
The area of interest is now inverted. As the fingerprint is monochromatic in this case, the image can be converted to a greyscale image at this point using the Greyscale Conversion filter from the Channels section.
Another Curve filter can now be applied to improve the contrast of the fingerprint a bit more.
1:1 Resizing
Let’s move on to one of the most important steps in fingerprint analysis: the 1:1 resize.
As previously mentioned, the dimensions of the image file must be adjusted so that any printout of the fingerprint is exactly the same size as the original trace. This step is also crucial for verifying whether the image resolution is sufficient for a comparison. As a general rule, the image should have a minimum resolution of 1000 DPI.
With the latest update of Amped FIVE (version 36648), the Resize 1:1 filter now offers the ability to perform this conversion while preserving the original pixel count. The 1:1 conversion is performed as follows.
We open the Resize 1:1 filter from the Edit filter group and draw a long, straight line along the scale present in the image. It is important to ensure that both endpoints (Point 1 and Point 2) are placed as precisely as possible in the center of the scale markings.
Next, we enter the World Distance in the Filter Settings tab—in our case, “3 cm”.
Under Output Mode, we select “Embed DPI Metadata.”
After clicking Apply, we can see that the output DPI value is “4878.4933”, which is well above the required 1000 DPI.
If we were to print the image now, the scale on the printed image would perfectly match the real-world scale used when the photo was taken. Additionally, we would retain the full resolution and all pixels from the original image.
Finally, if necessary, a text field with the case number can now be inserted into the image from the Presentation category using the Annotate filter.
A major advantage of Amped FIVE in the efficient analysis of large numbers of fingerprint images lies in how adjustments are managed through filters and filter chains.
In many cases, the evidence items or surfaces are very similar. For instance, this could involve a large number of banknotes bearing fingerprints, or multiple fingerprints on a single object photographed under consistent lighting and camera settings.
This means the resulting images share similar characteristics and can be processed uniformly. In Amped FIVE, adjustments made to one image can be quickly transferred to others simply by copying the filter via drag & drop to another chain. This significantly reduces processing time and ensures consistency.
When transferring adjustments to other images in this way, special attention must be paid to the Resize 1:1 filter. All images must be taken from exactly the same object-to-camera distance, otherwise the 1:1 conversion will be inaccurate
Isolating the Fingerprint from the Background
Let’s now take a look at a fingerprint where the color and pattern of the surface present a slightly greater challenge for us.
In cases where the surface has a colored or patterned background, it is often helpful to make targeted adjustments in the individual color channels to reduce distractions and improve fingerprint visibility.
In this case, we use the Channel Mixer filter from the Extract filter group and adjust the red, green, and blue channels accordingly, until the pattern on the surface is no longer visible.
As in our first example, we’ve applied the color channel adjustments selectively, limited to our region of interest.
In this case, the colored background pattern made it relatively easy to reduce the visual noise and enhance the visibility of the fingerprint.
But what should we do when both the fingerprint and the background pattern are monochrome?
Well, we’ll take the liberty of converting our original image to greyscale to simulate that scenario.
In such cases, another filter from the Extract filter group can help us: the Fourier filter. This filter transforms our image from the pixel domain into the frequency domain.
Within the filter, we can visualize the frequency representation and suppress the components responsible for the unwanted, periodic background patterns.
After applying the Fourier filter and making a slight global contrast adjustment, we achieve an image where the fingerprint stands out much more clearly from the background surface.
Let’s take our scenario with patterned surfaces one step further in this example.
What can we do when we’re dealing with a highly detailed and irregularly patterned background, such as this banknote?
At a certain distance from the surface, we can still make out the general shape of the fingerprint quite well. We can also see that many papillary ridges are visible.
However, as soon as we zoom in on the fine details we begin to struggle. The background pattern makes it extremely difficult to distinguish these crucial fingerprint details from the underlying design.
But even in this scenario, Amped FIVE offers us a solution.
We start by capturing two images:
- The first image shows the surface bearing the fingerprint.
- The second image is taken of a different £20 banknote, without any fingerprint, but with exactly the same camera-to-object distance and framing.
Before we can combine the two images, we first need to align them precisely using the Perspective Aligner from the Link filter group.
This step is essential, because even when utmost care is taken during image capture, the two photos may still be slightly misaligned by a few pixels. Such misalignment can significantly affect – or even completely prevent – the desired result: isolating the fingerprint from the patterned background.
After this step, we go to the Filter Settings and navigate to the Display tab.
There, we select the mode “Difference (Second – First)”, which gives us the desired result: a fingerprint that is almost completely separated from the background.
Now, we invert the image, just as we did in the very first example. This process leads us to our final result where all the fingerprint details are clearly and optimally visible.
In a final example, we will demonstrate how perspective correction can be used effectively when analyzing fingerprint images.
Perspective Correction
As previously mentioned, fingerprints should always be photographed parallel to the surface plane.
In some instances, for example when using specular lighting, it is not possible to view or capture a mark from a perpendicular position. In such cases, the use of the shift movement on a tilt-shift lens can avoid geometric distortion. If such a lens is not available, geometric distortion should be kept to a minimum and an angled scale such as the ABFO (American Board of Forensic Odontology) standard small scale should be used. The use of a geometric transform process should be considered to restore the resultant image, although this should only be used if the angle from perpendicular is less than approximately 25˚.
(Fingermark Visualisation Manual Second Edition 2022, Section 3.3.17)
The following shows how this workflow can be implemented in Amped FIVE if no tilt/shift lens is available.
Specular lighting is probably the most useful technique there is …
(Nick Marsh, Forensic Photography, A Practitioner’s Guide)
This lighting technique is particularly suitable for glossy and semi-glossy, non-porous surfaces.
The particular advantage of specular light is that the fingerprint can be visualized completely untreated. In this example, there is an untreated fingerprint on a bathroom tile.
The camera is now moved away from the parallel position and aligned at an angle of approx. 20 degrees to the plane on which the fingerprint is located.
When using the specular light technique, the light source is positioned in such a way that the reflection of the light source, as seen from the camera, is directly positioned above the fingerprint.
The image of the fingerprint that has now been visualized using specular light is open in Amped FIVE. In preparation for the Correct Perspective filter, lines are drawn with the Annotate filter that extends the markings on the ABFO scale. The Correct Perspective filter requires the definition of the four points of a rectangle. These are created by the intersections of the drawn lines.
It is very important that the drawn lines lie exactly on the markings of the ABFO scale.
Once the four points in the Correct Perspective filter have been determined, the filter can be applied and the perspective of the image is corrected.
As the previously defined four points form a perfect square, we can adjust the height and width in the input field so they are the same. This step creates the exact perspective as if the camera had been aligned parallel to the fingerprint.
To check whether the perspective is actually correct, the Annotate filter is used to create a circle that exactly matches the circle on the ABFO scale. This provides further strong confirmation that the perspective has been correctly adjusted.
Finally, we can enhance the contrast, convert it to grayscale and crop a smaller section of the image.
Conclusion
The digital analysis of fingerprints, especially in complex cases involving colored or patterned backgrounds, requires technical precision and a deep understanding of the tools available.
As demonstrated in the examples above, Amped FIVE offers a highly flexible and powerful environment for forensic image enhancement. From basic tonal adjustments to advanced frequency filtering and background subtraction, each step builds toward one goal: making the fingerprint as clear, detailed, and comparable as possible.
Throughout the workflow, certain principles remain constant: reproducibility, transparency, and respect for the integrity of the original trace. By combining methodical processing with forensic best practices, we are able to deliver results that are visually convincing, forensically sound and court-admissible.
Ultimately, it’s often the small details – as Sherlock Holmes rightly observed – that make all the difference in forensic fingerprint analysis. And with the right tools and a professional approach, even the most challenging fingerprints can be brought into clear view.
Alexander Fehrmann has an extensive background in forensic science through his work with German law enforcement agencies, where he specialized in crime scene investigation, forensic photography, and the documentation of physical evidence using advanced imaging techniques. A key area of his expertise involved the detection and photographic enhancement of latent fingerprints, particularly through the application of forensic light sources and multispectral imaging systems. During his tenure, he also served as a quality assurance officer, responsible for ensuring that fingerprint evidence met procedural and technical standards before its submission to the State Office of Criminal Investigation (LKA) for forensic evaluation.
