Collection of fingerprints:

Fingerprints (also includes palm prints and bare footprints) are the best evidence to place an
individual at the scene of a crime. Collecting fingerprints at a crime scene requires very few
materials, making it ideal from a cost standpoint. All non-movable items at a crime scene
should be processed at the scene using gray powder, black powder, or black magnetic powder.
Polaroid 665 black and white film loaded in a Polaroid CU-5 camera with detachable flash
should be used to make one-to-one photographs of prints which do not readily lift. All small
transportable items should be packaged in paper bags or envelopes and sent to the crime lab for
processing. Because of the "package it up and send it to the lab" mentality, some investigators
skim over collecting prints at a crime scene. Collecting prints at the crime scene should be
every investigator's top priority. Fingerprints from the suspect as well as elimination
fingerprints from the victim will also be needed for comparison (the same holds true for palm
and bare footprints).

Photography of fingerprints:

Perhaps the most common form of evidence collected at crime scenes is fingerprints.
Fingerprints should be photographed before they are collected on major cases or if the latent
may be destroyed when lifting. Occasionally, a latent print can be visible or developed on a
surface but cannot be lifted (e.g. a fingerprint in blood). In such a case photographing the latent
is the only way to document the evidence.

Normal black–and–white film was used to photograph this faint, dusted fingerprint.
High contrast film was used to photograph the same faint, dusted fingerprint.

Photography can also be used to bring out detail in a latent. Through the use of lighting, filters,
processing controls, and enhancement (in a program such as Adobe® Photoshop®) a faint
latent fingerprint can be enhanced. This is mostly done by building contrast between the latent
and its background.

Digital images

When photographing with a digital camera all photographs should be taken in color mode.
Even if the finished photograph would be better in black–and–white it should still be taken in
color when using a digital camera. By photographing in color subtle tones that could be lost
when photographing in black–and–white mode will be captured. Later the color digital
photograph can be changed into grayscale in a program such as Adobe® Photoshop®.

When photographing evidence containing fine detail with a digital camera it is highly
recommended the images be captured as RAW files. Raw files are unprocessed data directly
from the imaging sensor and saved in their true, 12 or 14 bit color depth. RAW files are read-
only files and must be converted to another type after they are processed. It is recommended
RAW files be enhanced (in a program such as Adobe® Photoshop®) and then saved as TIF
files.

Film

Well–defined fingerprints can usually be photographed with color film. However, black–and–
white film provides greater contrast than color film and is preferred for latent print
photography. The following is a list of a few black–and–white films that are suitable for latent
fingerprint photography.

Normal contrast photographs can be taken using a professional black–and–white film such as
Kodak T–MAX or Ilford Delta Professional films.

Some black–and–white films can be processed in color processing machines. In black–and–

white photographs all colors become shades of gray. This can be a problem when two colors
become nearly the same shade of gray in a photograph. However, colored filters can be used to
increase contrast between colors in black–and–white photographs. Color filters can build
contrast by either lightening or darkening the latent print, or by lightening or darkening the
background. To lighten a color, the color filter closest to the color is used. To darken a color,
the opposite color filter is used.

Black and White Contrast Filters

Objective: To increase contrast between colors that would normally photograph as nearly the
same shade of gray.

Light Information — White light is made up of a mixture of the primary colors—red, green
and blue. In theory red, green, and blue light sources simultaneously projected on the same
area will be white. Red and green light mixed together makes yellow. Green and blue light
mixed is cyan. Blue and red light mixed is magenta.

Light Transmission Law — The filter transmits its own color (lightened in the print) and
absorbs (subtracts) its complementary color (darkened in the print).

Selecting Black-and-White Films and Filters

to Obtain Contrast Between Colors
Black-and-white film and without any filter — the background and fingerprint record as
nearly the same shade of gray.
Black-and-white film and with a red filter —
the red filter transmits the red background providing needed contrast.

For example, a black powdered latent on a blue background would be difficult to see in a
black–and–white photograph. However, the latent print can be enhanced by causing the
background to lighten by using a blue filter. A ninhydrin developed latent on the back of U.S.
currency can be enhanced in two ways by using a green filter. The green ink in the currency is
lightened (the background is lightened) and the violet colored ninhydrin developed latent
fingerprint is darkened.

Procedures in Photographing Fingerprints

Establish the Location of the Fingerprint

The diagram and notes on a latent print card identify the original location of the fingerprint.

If you are going to photograph a fingerprint, the location of the fingerprint must be established.
While you could use mid–range photographs to show where each fingerprint is located in the
scene, the use of numerous mid–range photographs to show the locations of small items can
become confusing. A better technique is to forego the mid–range photographs and use the
diagram and notations on the latent print card to identify the original location of each
fingerprint. This can be done by including a scale in the close–up photograph of each
fingerprint. On the scale write the evidence item number that will be used on the latent print
card. Be sure the scale and the item number appear in the close–up photograph of the
fingerprint. Then the location of the fingerprint in a photograph can be related to a latent print
card on which the fingerprint’s location was diagramed and described.

Close–up Photograph

While there are specialized cameras designed for fingerprints, a 35 mm or good quality digital
camera with a macro lens or close–up accessory can be used for fingerprint photography.
Using a tripod helps with the positioning of the camera and also steadies the camera. This is
important since depth–of–field is shallow in close–up photographs. Precise focusing can be
made with a camera mounted on a tripod. Photograph the latent with the camera’s film plane
parallel to the fingerprint surface. In order to get as much detail recorded on the film as
possible, position the camera so the frame of your viewfinder is filled with the fingerprint and
scale.

Exposure

Some fingerprints can be photographed using ambient (existing) light. Ambient light exposures
of fingerprints with normal contrast can be exposed using the camera’s exposure system if the
fingerprint and its background are of normal reflectance. If the background is lighter or darker
than normal, then the exposure should be determined by metering off an 18 percent gray card.
For example, when photographing a black powdered fingerprint on a white background, the
camera will normally underexpose the photograph and detail in the photograph will be lost.
This is because most of the image is white and reflects more light than a normal background.
In such a situation you should meter off an 18 percent gray card to determine the correct
exposure settings.
In this photograph of palm prints the oblique angle of the flash was too low, creating shadows
in the textured wall covering. The shadows obscure the friction ridge detail of the palm print.

Artificial light (from electronic flash, flood lamps, flashlight, etc.) can be effective in
photographing fingerprints. Oblique lighting is used for most photographs of fingerprints. The
most effective way to insure you are using the best angles of lighting is “preview the
photograph” by looking at lighting from several different angles. To do this, position a strong
light source, such as a flashlight, at different angles to find the light angles that reveal the best
detail in the fingerprint. As you move the lighting you will see the results you will get by
looking into your viewfinder. At this point you can photograph the fingerprint using the
lighting from the flashlight or you can position your electronic flash at the best angles for the
photographs.

Whether using available light, electronic flash, or other illumination sources, bracketing of
exposures should be considered. Bracketing may reveal more detail in “low contrast” or faint
fingerprints. Underexposing the film will separate the steps on the white end of the gray scale.
Overexposure will separate the steps on the black end of the gray scale. The latitude for black–
and–white film is generally two f–stops underexposure and six f–stops overexposure.
Fingerprint on drinking glass using transmitted lighting — position a diffused light source
behind the glass.

Photographing Specific Types of Fingerprint Subjects

Dusted fingerprints with good visible detail can usually be photographed without special
lighting techniques.

Fingerprint impressions in soft substances (e.g., wax, putty, clay, adhesive tape, grease, or
dust) require the use of oblique lighting at a low angle. This will create small shadows in the
impression. Preview the effect with a flashlight.

Fingerprints on porous surfaces (textured wall coverings, wood, brick, etc.) may need almost a
90–degree lighting angle to avoid the creation of shadows in the surface’s texture, which
would interfere with the recording of fingerprint detail. Preview the effect with a flashlight.
Fingerprints on glass (windows, drinking glasses, etc.) can be photographed by placing a white
card behind the glass and using a low oblique angle of light. They can also be photographed by
using transmitted (back) lighting by positioning a diffused light source behind the glass.

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Fingerprint development using nanoparticles:
A large number of conventional methods have been used for the development and detection of
latent finger prints. However, these methods suffer from some limitations, that is, lack of
stability, contrast, and visibility.It may, however, be noted that certainty of a method for the
detection of latent fingerprint is limited. Therefore, there is a need for advanced as well as
selective methods for the detection of latent fingerprints. Over the past few years, a vintage
method, silver nitrate (AgNO3) has been used for the development of latent fingerprints which is
best suited for the porous surface like paper.
A novel solution of silver nanoparticles (AgNPs) has shown a glimpse to the better future of
identifying latent fingerprints. The mechanism of fingerprint development by silver nanoparticles
was first observed in silver physical developer (Ag‐PD) method. The Ag ‐PD method comprises
an oxidation–reduction couple where Fe+ ion reduces Ag+ ions to metallic silver (Ag0) which
produces a silvery image of fingerprint on paper surface.They reported that the development of
fingerprint on paper surface by this method was due to the physical interaction between silver
nanoparticle and fat‐soluble fingerprint residue. The possible mechanism for the development of
latent fingerprint by AgNPs comprises a physical interaction as reported in the existing literature,
where fingerprint residue gets positively charged and silver nanoparticle acquires negative
charge from their surrounding environment. When positively charged fingerprint residue(–
C=C–) comes in contact with negatively charged silver nanoparticles (due to the adsorption
BH4− ions), they attach themselves through an electrostatic force of attraction. Hence, physical
interaction of silver nanoparticles with sebaceous secretion of fingerprint residue leads to the
visualization of latent fingerprint on paper surface.
The previously reported data, fingerprints developed using silver nitrate has shown the highest
degree of stability with respect to the paper surface, where about 1–3% aqueous solution of silver
nitrate was utilized. Moreover, 1–3% aqueous solution of silver nitrate is made up from about
10–30 g of silver nitrate (Merck Grade) and the price of 1 g silver nitrate is approximately about
1,66 INR. Therefore, the significant rise in the cost of silver nitrate over the years has led
forensic experts to think very wisely before using it. Owing to this aspect, the current study
focuses on the minimal use of silver nitrate by lowering the concentration of silver nitrate. As we
decrease the concentration from 0.1 to 0.001 M, this will ultimately decrease the cost.