FS - Week 8 Lecture Notes

Topic = Crime Scene Photography

Fundamentals and Role of Forensic Photography

• Primary Functions of Forensic Photography:

  • Serves as an essential investigative tool and permanent recording mechanism.

  • Acts as a memory jogger for investigators, witnesses, officers, and medical personnel.

  • Used in court to support and corroborate verbal testimony and physical evidence.

  • Provides jurors with an accurate visual representation of the scene, items, and crime context.

  • Preserves transient evidence that would otherwise be altered, degraded, lost, or destroyed over time.

  • Documents exact item placement and spatial relationships of evidence within the crime scene.

Legal Standards and Admissibility Requirements for Court

• Core Evidentiary Criteria:

  • Accuracy: The photograph must be a true, fair, and accurate representation of the scene or object.

  • Relevance: The object depicted must be directly relevant to the legal issues at hand.

  • Non-Prejudicial: The photograph must not appeal solely to emotion or tend to prejudice the jury.

  • Fidelity: The photograph must be entirely free from optical, spatial, or perspective distortion.

• Digital Image Integrity and Chain of Custody:

  • Running Photo Log: Digital photos must be presented alongside a detailed running log documenting:

  • Date and time of capture.

  • Location of the scene.

  • Identity of the photographer.

  • Data Verification: Log entries must match the embedded digital metadata (EXIF) stored on the camera, hard drive, CD, or archival media.

  • Enhancement Rules: Original, unedited photographs must always be presented alongside any enhanced or processed versions.

  • Sequential Order: Photos must follow a strict, chronological sequential order.

  • Standard Operating Procedures (SOPs): Adherence to SOPs ensures compliance with image preservation protocols.

  • Access Control & Storage: Security software must restrict file access. Original master images must be saved as read-only files immediately upon transfer.

Crime Scene Field Protocols and Workflow

• Team Structure and Availability:

  • Typically staffed by $1$ to $2$ dedicated forensic photographers per scene.

  • Requires $24/7$ operational readiness and response capability.

• Scene Integrity Rules:

  • Scenes must remain completely unaltered prior to photography, except when immediate emergency medical intervention is required for injured persons.

  • No physical evidence collection or handling may occur prior to photographic documentation.

  • Comprehensive photography can reveal critical investigative clues and evidence relationships later in the case.

Digital versus Film Photography

• Foundational Mechanisms:

  • Both digital and film photography utilize light to form images.

  • Digital Sensors: Uses a Charged Coupled Device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensor.

  • Film Emulsion: Uses light-sensitive silver halide gelatin emulsion.

  • Modern police and forensic agencies exclusively utilize digital systems.

• Advantages of Digital Photography:

  • Instant Review: Immediate image feedback allows on-site quality and exposure verification.

  • Retake Policy: If an image is unsatisfactory, another photo can be taken immediately. Original digital files must never be deleted under any circumstances.

  • Operational Flexibility: Greater latitude in controlling exposure and image parameters.

  • Efficiency: Rapid point-and-shoot operation eliminates darkroom chemical processing delays.

  • Video Frame Capture: Individual high-resolution frames can be extracted from recorded video footage.

• Disadvantages of Digital Photography:

  • Increased scrutiny regarding image authenticity and susceptibility to digital manipulation challenges in court.

Image Quality Controls: Perspective, Focus, and Framing

• Eliminating Distortion:

  • Maintain good perspective by holding or mounting the camera level at eye level relative to the subject plane.

  • Prevent geometric tilting that distorts true physical dimensions.

• Focus and Clarity:

  • Sharp focus requires clean camera lenses and a stable camera platform (such as a tripod or monopod).

• Framing:

  • Frame the scene properly to capture necessary context without extraneous background distractions.

Forensic Lighting Principles and Angle Techniques

• Critical Role of Illumination:

  • Light direction dictates shadow creation, surface feature enhancement, and detail highlighting.

  • Alternate Light Sources (ALS) illuminate latent or hidden trace evidence.

• Angle-Specific Illumination Techniques:

  • $45^\circ$ Lighting: Uses $1$ to $2$ light sources positioned at a $45^\circ$ angle to the surface; minimizes harsh shadows; standard choice for general shape and size documentation.

  • $10^\circ$ Lighting: Positioned almost vertically ($10^\circ$ above the surface plane); eliminates shadows and surface texture.

  • Oblique Lighting: Low-angle light source placed nearly parallel to the surface; creates surface shadows that highlight subtle texture, depth, and three-dimensional details (e.g., footwear impressions, tire tracks, subtle bite marks).

• Specialized Lighting Methods:

  • Bounce Lighting: Bounces light off a reflective surface (e.g., umbrella, card, ceiling) to provide soft, non-glare illumination with low contrast.

  • Diffused Lighting: Passes light through a translucent diffusing material to soften harsh rays, eliminating hot spots and reflections on shiny objects.

  • Transmitted Lighting: Shines light directly through translucent or semi-opaque evidence (e.g., paper, thin fabric) from behind to create a shadow-free background and reveal internal structure or watermarks.

Forensic Photography Kit and Optics

• Camera Body Specifications:

  • Digital SLR (DSLR), or occasionally $35\,mm$ film bodies.

  • Minimum resolution sensor of $10\text{ megapixels}$ ($10\,MP$) or higher.

  • Requires full manual setting controls as well as automatic modes.

• Lenses:

  • Normal Lens: $50\,mm$ focal length lens, offering standard human eye perspective.

  • Wide-Angle Lens: $28\,mm$ focal length lens, used for photographing small rooms or confined indoor spaces.

  • Close-up / Macro Lens: Designed specifically for detailed images of physical evidence and small items.

  • Close-up Accessories: Lens adapters, extension tubes, and reverse-mount rings.

• Lens Mechanics and Optics:

  • Focal Plane: The lens gathers light from the object and focuses it onto the focal/image plane (the sensor) located behind the lens.

  • Focus Ring: Rotated manually to sharpen focus on the target subject.

  • Zoom Ring: Rotated to alter focal length and compose the frame.

  • Focal Length: The physical distance between the optical center of the lens and the image sensor.

  • Working Distance: The physical distance between the subject object and the front element of the lens.

• Proportional Relationship: Longer focal lengths require larger working distances:

  • $180\,mm$ macro lens $=$ $19\text{ inches}$ working distance.

  • $100\,mm$ macro lens $=$ $12\text{ inches}$ working distance.

  • $50\,mm$ macro lens $=$ $8\text{ inches}$ working distance.

  • Reversing and Stacking Lenses:

• Reversing a lens (mounting it backwards onto another lens or extension tube) transforms optics from minimizing to magnifying close-focus details.

• Close-up extension rings/tubes allow extreme magnification while maintaining adequate physical working distance.

The Exposure Triangle: Aperture, Shutter Speed, and ISO

• Aperture (f-stop):

  • Diaphragm opening size inside the lens controlling the quantity of light passing through.

  • Expressed as an f-number (e.g., $f/1.4$, $f/2.8$, $f/4$, $f/5.6$, $f/8$, $f/11$, $f/16$, $f/22$).

  • Inverse Relationship: A larger f-number indicates a smaller physical opening, permitting less light to enter.

  • Depth of Field (DOF):

  • Large aperture opening (small f-stop number like $f/1.4$, $f/2.8$) $=$ Shallow depth of field (only the target plane is in focus; background and foreground are blurred).

  • Small aperture opening (large f-stop number like $f/11$, $f/16$, $f/22$) $=$ Large/deep depth of field (maximizes focal sharpness from foreground to background).

• Shutter Speed:

  • Controls the temporal length/duration of sensor exposure to light.

  • Measured in full seconds or fractions of a second (e.g., $30\,s$, $1/15\,s$, $1/60\,s$, $1/125\,s$, $1/250\,s$, $1/500\,s$, $1/1000\,s$, $1/4000\,s$).

  • Motion Effect: Slow shutter speeds allow motion blur for moving objects; fast shutter speeds freeze rapid motion sharp in the frame.

• ISO Sensitivity:

  • Rating of the image sensor's sensitivity to light.

  • Lower ISO (e.g., ISO $100$, ISO $200$): Less sensitive to light, yielding fine grain and high detail clarity. ISO $200$ is standard in forensic photography.

  • Higher ISO (e.g., ISO $800$, ISO $1600$, ISO $3200$, ISO $6400$): Used in low-light environments, but increases digital sensor noise (graininess).

• Exposure Triangle Equilibrium:

  • Altering any single parameter (ISO, f-stop, or shutter speed) requires offsetting adjustments to the other two parameters to maintain balanced exposure.

Optical Filters, Flash Equipment, and Auxiliary Kit

• Forensic Filters:

  • Polarizing Filter: Cuts non-metallic surface glare, eliminates reflections from water or glass, and saturates colors.

  • UV Filter: Blocks ultraviolet haze in outdoor shots; under direct UV light, it captures fluorescent trace details.

  • Infrared (IR) Filter: Used with IR light sources ($\sim 900\,nm$) to reveal details invisible to human vision (altered documents, obliterated writing, gunshot residue on dark fabric).

  • Color Filters (Red, Yellow, Green, Orange): Isolate specific wavelengths to eliminate background interference or boost contrast (e.g., green filter for ninhydrin latent fingerprint development; red/yellow/orange filters for forensic staining).

• Flash and Support Gear:

  • Electronic Flash: Provides primary or fill lighting.

  • Remote Flash: Off-camera flash placement used for directional or oblique lighting.

  • Tripod: Essential for sharp focus during long exposures, low ISO settings, or overhead macro shots.

  • Locking Cable Release: Mechanically or electronically holds the shutter open during long exposures (e.g., bulb mode at night).

  • Log Book and Pens: For systematic real-time logging of camera settings, scene data, and photograph sequence numbers.

  • $18\%$ Neutral Grey Card: Provides a standard gray reference for accurate exposure metering and white balance calibration.

• Scales, Reference Markers, and Measuring Tools:

  • Linear rulers and tape measures for standard dimensional recording.

  • ABFO #2 Scale: An L-shaped (right-angle) precision reference scale developed by the American Board of Forensic Odontology featuring millimeter markings, gray scale swatches, and alignment targets. Crucial for bite mark and injury photography.

  • Index Cards / Evidence Tents: Numbered markers used to designate evidence items across photo series.

Evidence Photography Protocols and Scale Rules

• The Four-Photo Minimum Rule per Evidence Item:

  1. Overview Photo: Establishes the evidence item in its pristine condition as first discovered before any alteration.

  2. Mid-Range Photo: Documents the evidence item in relation to its immediate surrounding environment and spatial landmarks.

  3. Close-Up Photo: Captures close detail of the specific evidence features alone.

  4. Close-Up with Scale: Captures detailed measurement dimensions using an approved forensic scale.

• Scale Usage and Placement Guidelines:

  • Always capture two close-up photographs of evidence: first without a scale, then with a scale.

  • Purpose of Two Shots: Ensures the scale did not obscure underlying trace evidence, and proves in court that the item was not moved prior to measurement.

  • Plane Alignment: The scale must be placed on the exact same geometric/anatomical plane as the item being measured.

  • Proximity: Place measurement markings directly adjacent to the object without obscuring key features.

  • Material Selection: Choose appropriate scale types (e.g., avoid adhesive scales if trace evidence might be lifted or contaminated).

  • Prohibited Scales: Pens, coins, scrap paper, or uncalibrated objects are strictly unacceptable as forensic scales.

Scene Progression: Exterior and Interior Mapping

• Exterior Scene Protocols:

  • If structures are involved, always begin photography on the exterior.

  • Document the building structure, property perimeters, and immediate surroundings.

  • Capture all potential entry and exit routes, including doors, windows, and gates.

  • Outdoor open scenes: Capture landscape terrain and spatial markers.

  • Aerial photographs are highly beneficial for establishing broad spatial relationships.

• Interior Scene Protocols:

  • Document overall room layouts systematically.

  • Begin with a perspective shot from the main entrance doorway.

  • Capture the initial step-through perspective into the room.

  • 4 Corners Approach: Take overlapping photographs from each of the four corners of the room facing inward.

  • Include perspective views into adjoining hallways, stairwells, and adjacent rooms.

  • Record the exact locations and relative positions of all potential evidence items.

Crime-Specific Forensic Photography Protocols

• Homicide Investigation Protocol (13 Sequential Steps):

  1. Building exterior.

  2. External evidence locations.

  3. Primary scene entrance view.

  4. Room containing the victim.

  5. Adjoining rooms, hallways, or stairwells.

  6. Victim's body photographed from a minimum of $5$ distinct angles.

  7. Close-up photographs of all wounds and traumatic injuries.

  8. Weapons present at the scene.

  9. Trace evidence locations.

  10. Signs of activity prior to the crime (e.g., prepared food, open mail).

  11. Physical evidence of a struggle (e.g., overturned furniture, broken items).

  12. Line-of-sight perspectives from potential witness locations.

  13. Comprehensive autopsy photography.

• Suicides and Unexplained Deaths:

  • Process initially following standard homicide protocols. Document key mechanism items:

  • Ligature knots and binding methods (in hanging/strangulation).

  • Vehicle position, exhaust routing, and interior controls (in carbon monoxide gassing).

  • Original placement of suicide notes.

  • Prescription pill bottles and labels.

  • Illicit drugs, paraphernalia, or chemical substances.

• Assaults and Personal Injury Photography:

  • Capture the subject using vertical camera format.

  • Progression: Full-length body view $\rightarrow$ Head & shoulders view $\rightarrow$ Mid-range injury location shot $\rightarrow$ Close-up injury shot $\rightarrow$ Close-up injury shot with scale.

  • Bruise Documentation: Subcutaneous contusions may take up to $48\text{ hours}$ to fully manifest; often require UV or IR photography.

  • Bite Mark Protocol: Orientation photo first $\rightarrow$ Close-up shot taken from directly overhead ($90^\circ$ angle) with an ABFO #2 scale on the exact same plane; use diffused or oblique lighting. Never bend flexible scales over curved limb surfaces.

• Ultraviolet (UV) Photography for Bruising and Trace Evidence:

  • Wavelength: Filters restrict light capture to UV wavelengths below 400\,nm$.\n - **Penetration Depth:** Long-range UV light penetrates deeper into skin layers than visible light, providing high contrast and definition for deep subcutaneous tissue injuries.\n - **Camera Setup for UV Injury Shots:**\n - Shutter speed: 1/60\,s$.

  • Mount camera securely on a tripod.

  • Align camera parallel or directly overhead ($90^\circ$) relative to the injury.

  • Maintain a distance of approximately $30\,cm$ from the injury.

  • Capture visible light photos first $\rightarrow$ Take UV series with scale $\rightarrow$ Shoot across a range of f-stops ($f/5.6$, $f/8$, $f/11$) $\rightarrow$ Shift UV light angle and repeat shot series.

  • Additional Applications: Fluorescent latent fingerprints, body fluid secretions (semen, saliva, urine), invisibly marked currency, and stolen property.

• Vehicle Crime Scenes and Traffic Accidents:

  • Standard Vehicle Series ($8$ External Shots):

  • $2\times$ Direct front and direct rear shots.

  • $2\times$ Direct side elevation shots.

  • $4\times$ Corner shots at a $45^\circ$ angle.

  • Full interior photograph set.

  • Mid-range and close-ups of all external/internal damage or trace evidence.

  • Accidents and Hit-and-Run Scenes:

  • Final resting positions and orientations of all involved vehicles.

  • Positions of vehicles relative to one another and roadway landmarks.

  • Six Overview Photos: $2$ shots from each side directly aligned with the vehicle axles, and $1$ shot from each end.

  • Roadway debris, gouges, tire tracks, and skid marks.

  • Driver line-of-sight perspectives approaching the impact point.

  • Line-of-sight views from witness locations.

• Fire Scenes:

  • Because evidence removal is often impractical, photography must thoroughly document the entire structure.

  • Capture overall structural fire damage, adjacent structures, exterior ignition markers, burn patterns, melted appliances, and explosion debris fields.

• Property and Weapons:

  • Mandatory scale inclusion on the same plane.

  • Document class and individual characteristics: serial numbers, latent fingerprints, bloodstains, trace fibers.

  • Ensure a high-contrast, clean neutral background.

• Fingerprint Photography:

  • Must be photographed as a permanent record prior to any physical lifting attempt.

  • Dusted Latent Prints: Standard direct white light photography.

  • Impression Prints (3D in soft media): Low-angle oblique/cross lighting.

  • Porous Surfaces: Light source positioned at a $90^\circ$ perpendicular angle.

  • Glass / Transparent Media: Place a clean white card behind the glass; illuminate with oblique lighting.

  • Ninhydrin-Treated Prints: Photograph through a green filter to maximize background contrast against purple ninhydrin reactions.

• Footwear / Shoe Impression Photography:

  • Mount DSLR on a tripod with the sensor plane perfectly parallel to the impression surface.

  • Press scale into soft soil/media to the exact same depth as the deepest portion of the impression.

  • Apply oblique directional lighting from at least $3$ distinct angles.

  • Take mid-range and close-ups across multiple aperture settings.

  • Note: While photographic records are required, 3D casting yields superior structural detail.

• Bloodstain Pattern Photography:

  • Use oblique lighting to increase edge contrast.

  • Dark / Absorbent Media: Use Infrared (IR) photography ($900\,nm$ filter) to visualize bloodstains on dark clothing, denim, or carpet.

• Infrared (IR) Photography Applications:

  1. Questioned document examination (revealing alterations, ink differentiations, obliterations).

  2. Detection of secret, faded, or erased writing.

  3. Visualization of gunshot residue (GSR) patterns, biological stains, and weave irregularities on dark fabrics.

  4. Aerial photography (boosting terrain contrast, differentiating coniferous dark foliage from deciduous light foliage).

  5. Surveillance operations (coupled with thermal imaging).