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Crime Scene Investigation and Reconstruction

Fourth edition

Chapter 3

Crime Scene Photography

Objectives of Crime Scene Photography

Record the condition of the scene before alterations occur

Record the location and position of evidence items collected

Document the point of view of principals and potential witnesses

Document spatial relationships of pertinent items

Photography is…

Not a substitute for notes or sketches

An essential supplement to other modes of crime scene documentation

Crime Scene Photography

Photography also plays an important role in the efforts to reconstruct the events of the crime. In conjunction with sketches, photographs capture the physical aspects of evidence at the crime scene that are amenable to reconstruction by a qualified professional.

Capture the physical aspects of evidence at the crime scene

Issues

How many photographs to take?

Conditions at the scene create photography challenges:

Big outdoor crime scenes

Small crime scenes like bathrooms

Lighting issues like complete darkness

Smoke, fog, rain, etc.

A standard operating procedure should also be in place for all digital photography.

Cameras for Crime Scene Photography

The type of camera best suited for crime scene photography is the single lens reflex (SLR)

Important to have zoom lenses with macro capabilities

35mm is being replaced with digital single lens reflex (DSLR) cameras

Videotaping Advantages/Disadvantages

Advantages:

Provides a lifelike view to the viewer

The ability to instantly review the videotape at the scene

Disadvantages:

The addition of unnecessary detail

Lower resolution of the video camera as opposed to that of a still camera

Systematic Approach

To ensure that all necessary photographs are taken at the scene prior to any actions that may compromise the integrity of the scene

The sequence should be done by working from the perimeter to the center

This will facilitate the presentation of the photographs in the courtroom

Log all photographs taken in a photo log

Types of Photographs

Overview or layout (long range)

Medium range

Close-up

Point of view of witnesses

Night photographs

Latent impressions

Wounds

Position of Camera “Normal” to a Surface

Three Factors in Photography

To produce sharp images in the photograph, you need:

High quality lenses

High resolution of the image sensor in digital cameras

The correct exposure by the camera

Basic Camera Information

The Light Meter and Exposure—measures the brightness of available light

Lighting—flash cube, electronic flash, strobe etc.

Filters—used to provide special effects or eliminate unwanted glare

Camera Basics

Lens

Focal Length

Relates to depth of field

Determines if lens is wide angle or telephoto

Compound Lenses

Light passes through a series of “elements”

Camera Basics

The shutter - two basic types of shutter mechanisms:

The focal plane shutter, positioned just in front of the film

The leaf shutter, positioned either just inside the lens housing close to the diaphragm or behind the lens

The Shutter in Detail

The principal function of the shutter is to keep light from striking the film or image sensor in DSLRs

Shutter speeds marked on most modern cameras follow a sequence - 1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000, 2000, etc.

Camera Basics

Several factors affect the amount of light reaching the film, principally the duration of the exposure and the diameter of the aperture.

The aperture is the opening in the lens

Calibrated in f-numbers

Common f/stops are f/1.8, f/2.8/, f/4,/ f/5.6, to f/22 or even f/32

The Aperture in Detail

Controls depth of field

f/22 has great depth of field while f/1.8 would result in a very shallow depth of field

The Aperture in Detail

Apertures can range from 1.2 to 22. The larger the f-stop, the smaller the aperture; the smaller the f-stop, the larger the aperture.

F/stops are really fractions, like shutter speeds. (f/22 is really 1/22) f/22 f/5.6 f/1.8

Camera Shake

Camera shake (tremor, vibration) is the movement passed to the camera by involuntary hand and body tremor

This phenomenon can be minimized with

Long focal length lenses

Image stabilization (IS) in the lens (lens based) or camera body (body based)

Depth of Field

The zone both in front of and behind the focal plane that also appears acceptably sharp

Depth of field can be controlled because it is affected by changes in the aperture size

Digital Cameras

Digital cameras capture a digital image on a digital image sensor, also called an image processor

The image sensor is composed of pixels

A pixel is a single photosensitive unit (cell)

One megapixel equals one million pixels

Digital Cameras

Point-and-shoot digital cameras have a liquid crystal display (LCD) screen which acts as the view finder

DSLR cameras have an optical view finder and an LCD screen for viewing the captured images

The optical view finder is not affected by strong ambient lighting

Digital Cameras

Storage cards are of several types

The Secure Digital (SD) card -stores from one to eight megabytes

The secure Digital High Capacity (SDHC) card - stores from one to sixteen megabytes of memory

Digital Cameras - Image Resolution

Determined by:

Quality of the camera lens

Number of megapixels of the camera image sensor

In DSLR cameras, the image sensor is about 21.5 mm by 14.4 mm, larger than most point-and-shoot digital cameras

How to work with available light

When working in low-light situations, it is important to remember that our flash units can only travel a limited range, so we must work with light in the scene to assist us. If our eyes can see it then so can the camera.

ISO

Sutter Speed

Aperture (FStop)

The exposure triangle

Working with available light

Setting #1: sensitivity (known as the ISO)

ISO is the sensitivity of the sensor to the light. The higher this ISO setting, the more the sensitivity to light, thereby allowing that image sensor will work better in low-light conditions.

1. ISO (International Organization for Standardization [same as the old ASA, American Standards Association]): This speed value is based on an arithmetic scale.

A defect that occurs with too high of an ISO setting is called noise. When we used film cameras, this was known as graininess. Noise is the pixilation of the image that is seen when the image is enlarged and it appears to look like red and blue dots in the image. When photographing fingerprints, shoe wear, or other images, it is important that noise does not take away from the information or details of the evidence or scene being captured.

Setting #2: the shutter

There are two basic types of shutter mechanisms:

1. The focal plane shutter, which is positioned just in front of the sensor (hence the name) and is used almost exclusively in SLRs.

2. The leaf shutter, which is positioned either just inside the lens housing close to the diaphragm (in the case of the compound lens) or behind the lens (in the case of a simple lens).

The shutter speed is also known as the curtain. This is controlled in the camera. When we push down the button to take a photograph, the sound that is heard is the shutter. Shutter speeds are observed in fractions. So, when 500 is displayed, this really means 1/500. The faster the shutter speed, the less light you allow in.

A defect with too slow of a shutter speed is that we experience camera shake. The human hand can hold the camera steady for 1/50th of a second without camera shake (blurry images). Camera shake (tremor, vibration) is the movement passed to the camera by involuntary hand and body tremors, causing less sharp photographs.

Setting #3: the aperture/F-Stop

The aperture, also known as the F-stop (seen as an F with a number on the display, i.e., F4.0), is the opening in the diaphragm that determines the amount of light passing through the lens.

The range of apertures is 2.8–22 depending on the focal length of the lens. The higher the aperture setting, however, the less light you allow in and the more you close down the diaphragm opening (F22 lets in less light than F8).

It is important to note here that depth of field is directly affected by the aperture setting.

Depth of field

When a lens is focused on a point a certain distance away, there will be a zone both in front of and behind this point that also appears acceptably sharp on the film; this zone is called the “depth of field.”

Depth of field can be controlled because it is affected by changes in the aperture size.

With the aperture fully open F2.8), a lens has a small depth of field, and the further the lens is stopped down, the more the depth of field (F22).

Depth of field refers to the area that is in focus from lens to subject matter. The smaller aperture/F-stop number (f/2.8) correlates with a larger or wider aperture size, which results in a shallow depth of field. The larger aperture/F-stop number (F22) results in a smaller aperture size and therefore a deeper depth of field.

Latent fingerprints and patent impressions

Should always be photographed prior to lifting (without and with scales).

Use arrow directional in photographs.

Shoot photographs in the RAW format.

Photography of Wounds

Wounds should be photographed both before and after cleansing of the wound by medical personnel in the case of a living subject or by the forensic pathologist in the case of a deceased subject.

The wound site(s) and periphery should be searched thoroughly for any trace evidence before cleansing.

Infrared Photography

Uses infrared filters, which records images formed by infrared light

Used to locate alterations on documents

In aerial photographs it helps to locate gravesites

In the crime lab it is used to detect and document gunshot residue on bloody or dark fabrics

Infrared photography

Infrared photography uses designated infrared cameras or filters, which records images formed by infrared light.

Infrared photography is used in questioned document photography to locate and document alterations on documents, in aerial photography to assist in locating gravesites, and in the crime laboratory to detect and document gunshot residues on bloody or dark fabrics.

Ultraviolet Photography

Used to document materials that glow under ultraviolet light such as semen, certain fibers, and latent fingerprints dusted with fluorescent powders

Also used to photograph body wounds such as bitemarks

Additional photographic techniques

How to paint with light

Luminol/ Bluestar photography

QUESTIONS?

Discussion Question

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