Fingerprint Identification

Identification by fingerprints relies on pattern matching followed by the detection of certain ridge characteristics, also so known as Galton details, points of identity, or minutiae, and the comparison of the relative positions of these minutiae points with a reference print, usually an inked impression of a suspect’s print. There are three basic ridge characteristics, the ridge ending, the bifurcation and the dot (or island).




Ending Ridge

Identification points consist of bifurcations, ending ridges, dots, ridges and islands. A single rolled fingerprint may have as many as 100 or more identification points that can be used for identification purposes. There is no exact size requirement as the number of points found on a fingerprint impression depend on the location of the print. As an example the area immediately surrounding a delta will probably contain more points per square millimetre than the area near the tip of the finger which tends to not have that many points.



In image 1 we see part of a fully rolled fingerprint. Notice that the edges are cut-off so you can safely assume that this is not a fully rolled impression. If you take a look at image 2 you can see that I have sectioned out the centre portion of this impression and labelled 10 points of identification. That was not all the points found but simply the ones that could be mapped easily without cluttering up the image.



Image 2 when measured 1:1 is just over 1/4″ square. If you look closely you should be able to identify 10 additional points that were not mapped with the lines. In all I counted 22 points of identification on this 1/4″ square section of the impression. One thing to note here, you might be under the impression that making a fingerprint comparison is relatively easy but you should keep in mind a couple things.

First, image 1 and image 2 are both taken from the same image. In real life you would have impressions made at separate times and subject to different pressure distortions. Secondly, these images are relatively clean and clear where many of the actually crime scene prints are anything but clear. Last you have to consider that this is an easy comparison because you are blessed with having a core pattern and a delta when in some cases you may have a latent that could be a fingertip, palm or even foot impression.

Basic and composite ridge characteristics (minutiae)

Minutiae Example Minutiae Example
ridge ending bridge
bifurcation double bifurcation
dot trifurcation
island (short ridge) opposed bifurcations
lake (enclosure) ridge crossing
hook (spur) opposed bifurcation/ridge ending