003 CHS 3501 Chapter_16_Fingerprints

003 CHS 3501 Chapter_16_Fingerprints - 8/29/11 Fingerprints...

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Unformatted text preview: 8/29/11 Fingerprints Outline History 3 fundamental principles Classification members So what started all this interest? Wanted a way to identify people that was foolproof Anthropometry Alphonse Bertillon (1853-1914) developed what became known as anthropometry around 1883 (remember from the introduction lecture) The first systematic attempt at personal identification, which utilized detailed descriptions, photographs, and precise body measurements 1 8/29/11 Anthropometry Measurements Alphonse Bertillon standardized the mug shot, the evidence picture, and developed what he called photographie mtrique (metric photography) This system to allowed precise reconstruction of a particular space and the placement of objects in it, or to measure the object represented These pictures documented a crime scene and the potential clues in it prior to its being disturbed Bertillon used special mats printed with cadres mtriques (metric frames) which were mounted along the sides of these photographs Included were photographies strometriques (stereometric photographs), which pictured front and side views of a particular object Anthropometry Bertillon believed that in taking 11 precise body measurements along with systematic photographs a unique profile would result This was the first rigorous attempt at uniquely identifying individuals. Precursor to what we now know as biometrics However, labor intensive and susceptible to human error Best thing going for 20+ years 2 8/29/11 Sir William Herschel (1858) English administrator in India Began placing the inked palm impressions and, later, thumb impressions of locals on contracts. Used as a form of signature on the documents because of the high level of illiteracy and frequency of forgery Also began fingerprinting prisoners in jail Dr. Henry Faulds (1874) Scottish missionary doctor working in Japan First to suggest fingerprints do not change Tried to pioneer fingerprinting for criminal identification 3 8/29/11 Francis Galton Published Finger Prints in 1892 Finger Prints was the first publication to systematically cover the anatomy of fingerprints and methods of recording them Proposed classifying intro three pattern types: Failure of Bertillon System Will and William West Both at Fort Leavenworth prison around 1903 Looked like identical twins (and in fact they evidently were) Body measurements were indistinguishable Fingerprints clearly distinguish the two 4 8/29/11 Fingerprint Classification "Vucetich System" Dr. Juan Vucetich Argentina 1891... "Henry System" Sir Edward Richard Henry England 1897... Adopted by Scotland Yard (1901) Spanish-speaking countries English-speaking countries Fingerprint Fundamentals 1) No two fingers have yet been found to possess identical ridge characteristics 2) A fingerprint will remain unchanged during an individual's lifetime 3) Fingerprints have general ridge patterns that permit them to be systematically classified 5 8/29/11 Identification by fingerprints What is an identification? What is a class characteristic? How far can you go to declare an identification? Items at a crime scene sometimes constituting an identification Toolmarks Footprints Fingerprints DNA What else? Find Points of Comparison 6 8/29/11 Skin No identical ridge characteristics 7 8/29/11 Your book is Wrong! Ridge ending Bifurcation Island Short ridge Lake Hook or spur Bridge Double bifurcation Trifurcation Opposed bifurcations Ridge crossing All minute are... Ridge endings/beginnings Dots Bifurcations 8 8/29/11 Ridge Characteristics Type Lines, Delta, and Cores 9 8/29/11 Types Fingerprints remain unchanged "....friction ridge patterns remain unchanged naturally in their ridge detail during the lifetime of an individual. The ridge patterns begin to form during pre-natal life and are fully formed by the seventh month of fetal life." A. Moenssens, author of Fingerprint Techniques, 1971, and Fingerprints and the Law, 1969. 10 8/29/11 Ridge patterns can be classified Although friction ridge patterns exhibit an infinite variety of detail, they fall within certain broad classes that permit police to store and retrieve millions of prints on the basis of their general pattern: loops, arches, and whorls (L.A.W.) loops 60% arches 5% whorls 35% LAW... A loop must have one or more ridges entering from one side of the print, recurving, and exiting from the same side. If the loop opens toward the little finger, it is called an ulnar loop. If the loop opens toward the thumb, it is called a radial loop. All loops must have one delta, which is the ridge point at or directly in front of the point where two ridge lines (type lines) diverge. 11 8/29/11 LAW... Arches, the least common of the three general patterns, are divided into two distinct groups: plain arches and tented arches. The plain arch is formed by ridges entering from one side of the print, rising and falling, and exiting on the opposite side (like a wave). The tented arch is similar to the plain arch except that instead of rising smoothly at the center, there is a sharp upthrust or spike, or the ridges meet at an angle that is less than 90 degrees. Arches do not have type lines, deltas, or cores. LAW Whorls are divided into four groups: plain, central pocket loop, double loop, and accidental. All whorl patterns have type lines and a minimum of two deltas. A plain whorl and a central pocket loop have at least one ridge that makes a complete circuit. The double loop is made up of two loops combined into one fingerprint. An accidental either contains two or more patterns, or is a pattern not covered by the other categories. 12 8/29/11 Primary Classification Part of the Original Henry System and adopted by FBI 10-finger classification scheme Yields 1,028 Groups Simply based on presence or absence of whorl on each finger 13 8/29/11 Automated Fingerprint Identification Systems (AFIS) Implemented starting in the 1980's Digitally encode fingerprints based on mapping of minutiae: ridge endings and bifurcations. Database of "file" prints. Algorithms return a "candidate list" of best matches between "search" (unknown) and "file" prints Trained fingerprint expert makes final determination based on visual inspection 14 8/29/11 Automated Fingerprint Identification Systems (AFIS) Advantages: High-throughput, High speed "File prints" not limited to known suspects (e.g. FBI database has 35 million people in database) Challenges: Different suppliers have slightly different systems 15 8/29/11 Definitions Visible prints Made by touching a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink Plastic prints Ridge impressions left on a soft material such as putty, wax, soap, or dust Latent (or invisible) prints Impressions caused by the transfer of body perspiration or oils present on finger ridges to the surface of an object Latent fingerprints are made from perspiration, sweat, oils, and amino acids 16 8/29/11 Visualizing latent prints Surface Type Porous Non-Porous Surface Examples papers, cardboard, cloth glass, mirror, tile, painted surfaces Visualization Methods chemical development: I2, Ninhydrin RUV, fingerprint powder Super Glue Locating latent prints RUVIS: Reflected Ultraviolet Imaging System Locates prints on non-porous surfaces by aiming UV light at surface. The reflected-back image is converted to visible light by an image intensifier. Latent print on sticky side of duct tape Latent prints on painted wall Illustration of Contrast Effect due to variation of illumination angle. Depending on what angle the user holds the light, a print can either appear white or black. 17 8/29/11 Visualizing latent prints Fingerprint Powders used for non-porous surfaces lightly applied with camelhair or fiberglass brush adheres to oils/residue of fingerprint available in a variety of colors goal is have good color contrast with background surface; gray and black powder common Visualizing latent prints Other types of fingerprint powders Magna brush / magnetic-sensitive powder -- for sensitive prints that might be damaged -- good for slightly textured surfaces: leather, plastic Fluorescent powders -- designed to fluoresce under UV light -- creates better contrast with background surface color. 18 8/29/11 Chemical Visualization for Porous Surfaces Iodine fuming oldest method sample is placed in developing chamber heated I2 (s) I2 (g). "sublimation" visualization fades, "fix" stain with 1% aqueous starch solution. Ninhydrin forms a purple-blue color by reacting with trace amounts of amino acids in prints applied as a 0.6% solution in acetone visualization can be sped up with heat Chemical Visualization for Porous Surfaces Physical Developer silver-nitrate based liquid reagent destroys proteins, so should be used only after ninhydrin is attempted Ninhydrin substitutes such as DFO (1,8-diazafluoren-9-one) (left side) image and IND (1,2- Indandione) (right side image) Viewed under green light, through a dark orange filter 19 8/29/11 Chemical Visualization For non-porous surfaces (e.g. metals, electrical tape, leather, plastic bags, etc.): Super Glue (cyanoacrylate) fuming typically done in a chamber glue is heated to form a vapor vapor reacts to produce a whiteappearing print also combined with fluorescent dyes to aid visualization (e.g. rhodamine 6G) Fingerprint developed with cyanoacrylate, cut in half and stained with Rhodamine 6G (left side) and Basic Red 28 (right side) Alternate light sources "Crime-scopes": Visualization based on fluorescence. Portable, high-intensity quartz halogen, xenon, or indium light sources Can be focused on area via fiber optic cable Can be passed through filters to aid visualization 20 8/29/11 Preservation of Developed Prints 1) Once print has been visualized, a photograph should be taken before any further attempts at preservation. -- Adapters can generate 1:1 scale images 2) If object can be transported, lay clear tape over print to preserve it. 3) More commonly, "lift" the print with lifting tape. -- then place lifting tape on card with good background contrast Digital Imaging and Enhancement of Prints Problem: Developed latent prints from a crime scene are typically imperfect. Solution: Photographic fingerprint images are scanned/ digitized and once stored can be enhanced electronically for better visualization. Potential risk: The process of digital manipulation might improperly alter image resulting in faulty analysis 21 8/29/11 Digital Imaging Concepts Pixels ("Picture elements"): Square electronic "dots" which comprise image file Bit depth: the number of bits used to define each pixel. The greater the bit depth, the greater the number of tones (grayscale or color) that can be represented (e.g., 12-bit = 4,096 tonal variations) Resolution: Represented as "pixel dimensions" (i.e., 800 x 600), or "dpi" Digital Image Enhancement FFT: "Frequency (or fast) Fourier Transform" used to subtract periodic or repetitive background patterns such as lines or dots 22 ...
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