The underside of the fingers and palms, as well as the soles and toes of the feet are lined with raised lines of skin called friction ridges. The tops of these ridges are dotted with pores through which perspiration is discharged. This perspiration tends to coat these ridges causing them to become moist and when an object is touched the outline of these ridges in moisture may be left. This is the traditional latent print.

    The phrase, "...may be left..." is used because a latent print is not left each and every time something is touched. In order for the outline of the ridges to be transferred, the ridges must bear some substance, such as moisture, grease, oil, etc. If the ridges are dry and the surface is dry, no transfer will take place. It also occurs that even though a transfer does take place, the latent is not sufficient to be of value for comparison purposes due to its fragmentary nature or lack of clarity. In the real world it is not like the television program, CSI where beautiful latent prints are always developed and then immediately identified.

    It is true that no two fingerprints are alike - even twins, triplets, etc. Technically, we would say that the ridge arrangement on each finger (palm, foot) of each individual is different and that this ridge arrangement does not change naturally from before birth until decomposition after death. But it all boils down to the same thing; all fingerprints (palm prints, footprints) are different.

    Fingerprints are compared by (1) determining if there is similarity in the ridge flow (2) noting the arrangement of the ridge characteristics (ending ridge, bifurcation and dot) in each print and determining if they match and (3) observing the ridge structure in both prints. The critical portion of the comparison process is number 2 - the ridge characteristics. It has long been debated as to how many of these matching characteristics must appear in the same relative position in both prints before it can be declared that they are the same. The standard answer that is most often given is, "There is no minimum number. Therefore as each latent print is judged on its own merit, the latent print in question must be examined before it can be determined weather or not it contains sufficient ridge detail." In reality, each fingerprint examiner (expert) does have an approximate minimum number and it generally fluctuates at between 7 to 9 characteristics, depending upon factors such as clarity and uniqueness. These ridge characteristics are commonly known in the fingerprint community as points of identity, or simply points.