What are some methods done by latent fingerprints? What are some advantages and

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In forensics, latent fingerprints are marks left at the scene of a crime which may not be immediately visible to the naked eye. To expose latent fingerprints, technicians use fingerprint powder, fuming, and other techniques. Identifying latent fingerprints is an important part of evidence collection, and many technicians specialize in retrieving fingerprints from crime scenes and analyzing them in the lab in order to assist law enforcement with apprehending criminals.The hands and feet are covered in a natural secretion, due to the eccrine glands, which produce sweat, a mixture of water, salts, and other trace compounds. The sweat adheres to the friction ridges of the finger, and when a finger is placed on a surface such as glass, plastic, or wood, an impression known as a fingerprint will be left behind. The natural secretions of the body preserve the fingerprint, which is utterly distinct; no two humans have the same fingerprints.Latent fingerprints are usually left behind by accident, because a careless criminal did not realize that his or her hands might leave a mark. Sometimes, fingerprints are made from substances other than sweat such as blood, other body fluids, or paint. In this case, they are called patent fingerprints. Part of the analysis performed on fingerprints includes a determination of what the fingerprint was made from, as this may provide additional evidence about the criminal or the crime. METHODOLOGY First, we processed the items of evidence utilizing the traditional iodine fuming technique. For this research, an iodine fuming wand was used. The items were then photographed using a Fuji S2 Pro mounted on a photography table with adjustable height track and standard side-lighting. A scale was used in the first picture. Next, without moving the item of evidence or changing any of the lighting conditions, we removed the scale and took another picture after the iodine had dissipated. Iodine will dissipate over time, at least 24 hours, or it can be sped up to a matter of minutes by placing a source of ammonia fumes near the item. The primary consideration at this stage involved insuring that the item of evidence had not moved, and that the lighting conditions on the first photograph were the same as those on the second photograph. After both photographs were taken, they were brought into Adobe Photoshop. For this experiment, Adobe Photoshop CS2 was used. The following procedure and settings can be used to duplicate our methods: With both images in the working window, select the image with the scale. Select Image > Calculations. A Calculations window will now appear. Source 1 will be the image with no scale and source 2 will be the image with scale. The channel that has worked the best in our research has been the blue channel. However, depending on the colors in the background, a different channel might be preferable. Blending will be set as Subtract. Opacity should be set to 100%. Offset can be set from 65 to 100 depending on the requirements of the image. Scale should be set to 1. Result should be set to New Channel. Once these steps have been completed, click OK and a new channel will appear in the Layers Window. Select this channel “Alpha 1,” and then select Image > Mode > Grayscale. At this point, all of the usual enhancements such as brightness, contrast, levels, etc. can be adjusted to the criminalist’s preference. Advantages of this method include: The technique is relatively easy to learn and utilize. Costs associated with the technique are minimal if Adobe Photoshop is already being utilized. The latent image remains undamaged by this process so other development processes can subsequently be utilized. Disadvantages of this method include: This technique can be a bit time-consuming as the visual image can take some time to dissipate. The visual image must completely disappear from the “loud” background prior to taking the second photograph. Lighting and positioning of the evidence item must be strictly maintained and controlled for both the photo with the visible print on the “loud” background and the subsequent photo of just the “loud” background.

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