It is well accepted that fingerprints are unique to each individual and can thus be used for identification. In evidence, prints can be visible or not, dependent upon the particular piece of evidence being analyzed. If the prints are not visible, electronic, physical, and yes, chemical processing allows the print to be visualized. Once visualized, the technician must then provide a comparison report to determine if the prints are a match to a suspect's prints. Print comparison is now run digitally, but unlike the depiction on CSI, computer searches only produce some probable suspects. The real identification and comparison is generally done visually by hand.
Fingerprints are the friction ridge patterns found on the fingers, palms, toes and soles of the feet. Fingerprints or prints in general are composed of ridges and valleys:
Black lines are ridges and white lines are valleys. The pattern that appears on the fingerprint is based on genetics and is unique to an individual. Even identical twins have differing fingerprints.
Fingerprints are categorized by what is called pattern and minutiae.
Modern computer software is programed to look for and compare these minutiae. The database called the Automated Fingerprint Identification System or AFIS is used throughout the United States to search for comparison prints that have been logged into the system with identifying patterns and minutiae identified. If you have ever been fingerprinted for any reason (legal or illegal), your prints are probably in this system.
There are 3 types of fingerprints that can be collected and analyzed: