A fingerprint is an imprint formed when the surface of the palm of the hand is in contact with any surface. This kind of imprint is composed of an arrangement of different patterns formed by the raised parts (called ridges) and recessed parts (called grooves) of the fingerprint. Because of the random arrangement of these pattern features, each person's fingerprint is unique. Because fingerprints are unique, universal, permanent, non-imitable, classifiable, and can be found in almost all properties of crime scenes, development and preservation are crucial. ("Virtual Lab", 2021). In terms of fingerprint preservation, methods such as casting materials, latent printing enhancement, and photography techniques are mainly used.

Forensic photography needs to record the evidence found at the crime scene. Even if forensic photography is taken during the marking, collection, and preservation of the crime scene, or in the laboratory during analysis, it will permanently record the evidence at the crime scene. When comparing microscopic or fragile evidence, enlarged photographs prove useful. Recording physical evidence through photography makes it easier for multiple people to analyze the evidence at the same time. Of course, photo files can mitigate the impact of damage or loss of evidence. (Rethykl, 2001)

At least in the last century, the New York-based Folmer & Schwing Manufacturing Company created the first camera dedicated to fingerprint recognition. Install the fixed lens and lamp in the oval housing, the camera is completely independent. The light is activated by the shutter movement, exposing a 2 inch x 3 inch glass plate, and the lens is located at a specific point to produce a focused life-size image (1:1) on the film. (Lightning Fan Company, 2003). The open end of the rectangular camera is placed on the print, and the exposure button is pressed to take the picture. (Hutchins, 2014)

During forensic investigations, it is vital that destructive testing does not destroy or change any evidence, especially in the early stages of determining the properties of the material.

Especially in the case of fingerprints, if fingerprints are found on challenging surfaces, or in the case of making plastic fingerprints, accidental damage or loss of details may occur, and such damage may be hidden during the investigation process. Key data.

Photography procedures for photos found at the crime scene

Determine the position of the impression

It is easy to identify patents and plastic prints at the crime scene. On the other hand, hidden seals are often overlooked. To avoid considering all possible contact surfaces, such as entry and exit points, door handles, tables, plates, etc.

Once positioned (with scale), medium or close-up photos should be used to record the exact position of the fingerprint relative to its surrounding surface. (Stages, 2021).

Exposure: Some patented prints can be photographed using ambient (natural) light. However, depending on the background, the contrast may be adversely affected. For example, when shooting a black powder fingerprint against a white background, the camera will underexpose the image, resulting in loss of detail. The image reflects more light than a typical background because it is mostly white.

The light source can be a photographic laboratory light, a photographic slide viewer, an electronic flash, a forensic light source, or a photographic negative observation light. (Stages, 2021)

The latent print card showing the original position of the fingerprint. (Stages, 2021)

Direct lighting: This is a strong light that comes directly from a light source instead of reflecting off another surface. This lighting technology provides a great contrast between the light and dark parts of the subject. 2 or 4 lights are balanced and aligned 45 degrees above the object to directly illuminate it. (Hutchins, 2014)

Direct reflection lighting: In direct reflection lighting, a light source is 10° away from the object, and the object is 10° away from the lens system. The method works best on flat surfaces and makes a lot of difference with respect to the surface. On a light gray (white) background, latent print photos developed with black, gray or silver powder will always be taken as dark (black). (Hutchins, 2014).

Frontal directional lighting: In frontal directional lighting (axial or axial lighting), the light source is placed at right angles to the axis of the camera lens. The subject is placed directly in front of the camera lens. In order to direct light to the object, a piece of glass is placed at a 45-degree angle to the camera lens axis. This technique is used to photograph latent marks on a mirror or marks inside a sickle. (Hutchins, 2014)

Cross lighting / oblique lighting: also known as side lighting. In order to create shadows that show details, low-angle lighting is used. The light source is placed at a low or oblique angle, sweeping the entire surface and emphasizing elevated areas. If shadows become a challenge, a second light is needed. It is used for "plastic" or 3D impressions on surfaces such as wax, clay, soap, butter, soil, etc. (Hutchins, 2014)

Even if there is a specific camera for recording fingerprints, you can use a 35mm or high-quality digital camera with a macro lens or any other close-up accessories for photography. Use a tripod to achieve the positioning and stability of the camera. This is very important because the depth of field of close-up photography is very shallow. The camera mounted on a tripod can achieve precise focusing. In order to capture the greatest detail, take a photo of the latent image so that the surface containing the print is parallel to the film plane of the camera. To get as much film detail as possible, fix the camera at a specific point so that the fingerprint and scale occupy the frame of the viewfinder. (Stages, 2021)

In many cases, photography will be a more practical way of identification. In situations where evidence preservation is critical, fingerprint photos may be useful. This allows obtaining proof of identity before collecting evidence without causing any discomfort to the deceased. (Shafer and Frost II, 2021)

The main goal of any challenge is to address the fair and accurate representation of photo evidence.

Fingerprints have been successfully extracted from photos many times. It is reliable because in the case where the fingerprint is obtained from the "attached photo", the details of the friction ridge will not be deliberately changed.

The fingerprints extracted from these photos have the following benefits-

There is software available to track, zoom, compare, enhance, and print work from multiple investigators and sources. In digital imaging, image enhancement is achieved by the scanner evaluating the pixels around each new pixel to determine what color the higher resolution image should be. (Rethykl, 2001).

In the case of a decayed body, this is also the preferred mode for handling and recording fingerprints. In the late stages of decomposition, when the skin is dry or requires maceration, removal of the epidermal layer of the skin may be worrying. (Shafer and Frost II, 2021)

Because the fingertip is a convex surface, different degrees of oblique lighting are often used for photography of the details of the finger's rubbing ridge. The best strategy for the brightness and lighting angle of each individual print is usually obtained through trial and error, taking pictures of each finger to narrow the range. (Shafer and Frost II, 2021)

Use strong oblique light (Schaefer & Frost II, 2021)

Disaster victim identification is another area where this technology is beneficial (DVI). At the scene of any major disaster, it is crucial to retrieve, identify and return the remains to the investigators and the families of the deceased. There is usually a time delay between the discovery of the dead or parts of the body at the disaster site and the inspection in the morgue. (White, 2021)

        Decompose the visible details of the image of the finger for comparison after shooting

Detectives received information that Dannie Horner, a resident of Sarasota, was making child pornography with a 1-year-old child. However, even if Horner is arrested, the authorities still need evidence to prove their case. Investigators found photos of Horner and the victim while sorting through the photos on the phone; Horner’s face is not visible in any child pornography pictures, but he can be seen holding the camera in one hand and the other Hand abuses children. Horner was already a suspect in the case, so he manually compared the fingerprints he archived with the fingerprint details seen in the photos recovered from the phone. Since Horner is an artist by profession, his fingerprints are stained with paint, so detectives use computers to isolate and extract them. It turned out that this was a perfect game. (Chen, 2021)

Visible details after extracting finger ridge details from the defendant's photo (Schaefer & Frost II, 2021)

Scientists at Japan's National Institute of Informatics (NII) recently stated that they can extract usable fingerprints from photos of bare fingers taken up to three meters away. (Miura et al., 2016)

Of course, it is difficult to identify individuals based on the friction ridges visible in the image. The fact that the image in question and the known impression are not calibrated to scale is one such challenge. (Grice & Turnidge, 2021)

When checking fingerprints, the pattern area of ​​the finger or the palm rest is the most critical, but when extracting the fingerprint from the attached photo, the suspect’s finger may be occupied by any object, such as holding a gun, grabbing a basketball stick, etc., which may not be possible. The pattern area is obtained, so the forensic scientist may have to print with discrete parts. (Karen Oswald, sponsored by NIJ, 2020). Distortion is usually caused by the focus and light of the photo. Since you have to use the provided content, it is difficult to extract fingerprints from photos with ineffective focus and unfavorable light exposure. (Karen Oswald, sponsored by NIJ, 2020)

Another objection is that digital images are easy to manipulate and difficult to detect. For the same reason, the authenticity of digital photos is always questioned in court compared to photos taken with analog cameras.

With the advancement of camera and electronic image resolution technology, it has become more and more common to randomly capture friction ridge skin in relatively high-quality images. The popularity of social media sites such as Facebook, Instagram and Twitter has led to a large number of public photos. If investigators know what can be done, we can expect to see an increase in such identification in criminal investigations.

Although there are many controversies about the manipulation that can be performed using modern Photoshop technology, it must be pointed out that in most cases, the incidental or evidence photos seized by the investigative team are unlikely to be manipulated because the perpetrators did not expect this to happen. Condition. action plan.

When examining such photos, we should also be aware of any potential contextual or background biases that may affect the results of the investigation.

Pooja Chandran has a Master of Forensic Science from the Institute of Forensic Medicine in Bombay, specializing in suspicious documents, fingerprints and forensic physics.

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