Crime Scene Investigator Network Newsletter

Most law enforcement agencies either have AFIS or have access to AFIS. Most AFIS systems will accept latent fingerprint images at 1:1 or 5:1 ratios. Creating 1:1 or 5:1 images of a latent lift with a copy camera (e.g., the MP-4 Polaroid) is easily accomplished. Another effective way to acquire a 1:1 image of a lift is through the use of a flatbed scanner. However, occasionally the AFIS operator may encounter a photograph or an image that was not captured at a 1:1 ratio (film or digital), and the image needs to be resized for AFIS entry. The following report describes methods to capture 1:1 photographs with a copy camera and also describes a simple way to resize images that were not taken at a 1:1 ratio.

Copy Camera

To establish a 1:1 ratio on any copy camera, adjust the bellows so that the optical center of the lens is twice the focal length of the lens from the film plane (e.g., 135 mm x 2 = 270 mm). On the commonly used MP-4 camera, this equates to setting the bellows at approximately the 22.1 mark when using the 135 mm lens. The distance from the lens to the surface should also be twice the focal length of the lens. The proper distance is easily established by opening the lens aperture at its largest opening and adjusting the camera position up or down until the image comes into focus. Using a ruler, a test photograph can verify the accuracy of the setting (Figure 1). Minor bellows adjustments should be made as needed to adjust the magnification (extend the bellows to increase magnification). Once the correct position on your MP-4 has been determined, the image should always be accurate when using that lens bellows extension setting. The thickness or height of the latent on the item does not matter. The camera height is adjusted to accommodate the variation in the height of a latent on the evidence.

Scanning Photographs

The original photograph must include a scale in the photo. Align or rotate the photograph so that the scale will be scanned in either a vertical or horizontal orientation. Set the scan resolution as recommended in your AFIS system specifications. (It is necessary to scan photographs at a higher resolution if the photograph is printed at less than a 1:1 ration.) Complete the scan and save the image.

Most consumer imaging software programs are capable of the functions needed to resize an image to the proper scale. Some minor variations in the names of the commands and functions may occur, but the functions should be similar. Click on Open File, find the image you just saved, and open it. (I suggest that you have at least 1" visible on the scale in your image.)

Select the Crop tool from the tool bar. Click and drag corner to corner to make a box. Move the box so that one of its sides lines up with the 1" marker you have chosen to be the edge of your image (Figure 2). Now you can enlarge or reduce the size of the box by clicking the other side of the box and dragging until you have sized the width (or height) of the box to 1" (or whatever size you will need to include all of the desired latent print). You can be more precise if you zoom in. If you are satisfied that the size of the box is accurate, click inside the box and drag the box so that the box is centered over the latent fingerprint (Figure 3). Your image will now be 1" wide.

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