Forensic Photography Basics
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1
What is the primary scientific purpose of forensic photography?
To create an accurate, reproducible visual record of evidence, scenes, and relevant conditions for examination and legal proceedings.
2
What is the exposure triangle in photography?
The relationship among aperture, shutter speed, and ISO setting in controlling image brightness and photographic results.
3
What is aperture in a camera lens?
The adjustable opening through which light passes toward the image sensor or film.
4
What does an f-number represent?
The ratio of a lens's focal length to its effective aperture diameter.
5
How does changing from f/8 to f/5.6 affect light transmission at the same shutter speed?
It increases the light admitted by approximately one stop, or about twice as much.
6
How does changing from f/4 to f/8 affect light transmission at the same shutter speed?
It decreases the light admitted by approximately two stops, or to one-quarter as much.
7
What is shutter speed?
The duration for which the camera sensor or film is exposed to light.
8
What happens to exposure when shutter time changes from 1/125 second to 1/250 second?
The exposure time is halved, reducing the light collected by one stop if other settings remain unchanged.
9
What is ISO in digital photography?
A camera sensitivity or exposure-index setting that influences the brightness produced from a given exposure.
10
What is the tradeoff of using a high ISO setting?
It can permit imaging in lower light but may increase visible noise and reduce image quality.
11
What is depth of field?
The range of distances within a scene that appear acceptably sharp in an image.
12
How does a smaller aperture generally affect depth of field?
It generally increases depth of field when other relevant factors remain constant.
13
How does focusing closer to an object generally affect depth of field?
It generally decreases depth of field at a given aperture and focal length.
14
What is focal length?
An optical property of a lens that influences image magnification and angle of view.
15
How does a shorter focal length generally affect angle of view on the same camera sensor?
It produces a wider angle of view.
16
What is a macro lens?
A lens designed for close-up photography with relatively high reproduction magnification.
17
What does a 1:1 reproduction ratio mean?
The subject is projected onto the image sensor at approximately its actual physical size.
18
Why is a tripod useful in forensic close-up photography?
It stabilizes the camera and reduces motion blur during precise framing or longer exposures.
19
What is camera shake?
Unintended camera movement during exposure that can reduce image sharpness.
20
What is motion blur?
Image blur caused by movement of the subject or camera during exposure.
21
What is a photographic scale?
A ruler or calibrated reference placed in the same plane as relevant evidence to document its dimensions.
22
Why must a photographic scale be positioned in the plane of the evidence?
Differences in distance or angle can introduce perspective and measurement errors.
23
What is a perpendicular evidence photograph?
An image taken with the camera's optical axis approximately perpendicular to the evidence plane.
24
Why is perpendicular photography preferred for many two-dimensional impressions?
It reduces perspective distortion and improves the reliability of dimensional comparisons.
25
What is perspective distortion?
An apparent change in object shape or relative dimensions caused by viewing geometry.
26
What is lens distortion?
An optical effect that causes straight lines or object shapes to appear altered, such as barrel or pincushion distortion.
27
What is white balance?
A camera adjustment used to render colors appropriately under different illumination conditions.
28
What is a color reference chart?
A standardized set of colors used to assess or calibrate color reproduction in photographs.
29
What is oblique lighting?
Illumination directed at a low angle across a surface to emphasize texture, relief, or shallow impressions.
30
Why is oblique lighting useful for footwear impressions or toolmarks?
It creates shadows and highlights that can reveal three-dimensional surface detail.
31
What is transmitted-light photography?
Photography using light passing through an object or material toward the camera.
32
What is reflected-light photography?
Photography using light that strikes a subject and reflects toward the camera.
33
What is cross-polarized photography?
A technique using polarizing filters on the illumination and camera to reduce certain surface reflections.
34
What is fluorescence photography?
Photography of light emitted by a substance after excitation with an appropriate light source.
35
Why are barrier filters used in fluorescence photography?
To reduce excitation light reaching the camera while transmitting the desired emitted fluorescence.
36
What is a RAW image file?
A file containing minimally processed image sensor data together with relevant camera information.
37
Why can RAW capture be valuable in forensic photography?
It preserves greater flexibility for controlled image processing and may retain more original sensor information than a processed JPEG.
38
What is a JPEG image?
A widely used digital image format that typically applies lossy compression to reduce file size.
39
What is lossy image compression?
A process that reduces file size by discarding some image information, potentially affecting fine detail.
40
What is image metadata?
Information associated with an image file, such as camera settings, timestamps, device details, or processing history.
41
What is EXIF metadata?
Exchangeable Image File Format information commonly stored with photographs, including certain camera and exposure details.
42
Does a timestamp embedded in an image file independently prove when the photograph was taken?
No. Camera clocks, software, and metadata editing can affect recorded timestamps.
43
What is a cryptographic hash of a digital photograph?
A computed value used to help verify whether the digital file's contents have changed.
44
Why should original forensic image files be preserved?
They provide a reference for evaluating authenticity, processing steps, and any later changes to the images.
45
What is non-destructive image enhancement?
Processing that preserves the original file while creating separately documented adjusted versions.
46
Scenario: A close-up photograph of a fingerprint is sharp in the center but blurred near the edges because the evidence plane is tilted. What is a suitable correction?
Align the camera more nearly parallel to the evidence plane and use an appropriate aperture and focus setting.
47
Scenario: A photograph of a footwear impression has a ruler several centimeters above the impression surface. What problem may result?
The ruler may not provide an accurate dimensional reference because it lies in a different plane.
48
Scenario: A dimly lit scene requires a long exposure. What equipment can reduce camera movement?
A stable tripod and remote release or equivalent camera-triggering method.
49
Scenario: A forensic photograph was brightened and sharpened for courtroom presentation. What documentation is important?
Preserve the original image and record the enhancement steps so the result can be evaluated independently.
50
Scenario: A digital photograph has no EXIF metadata. Does that establish that the image is fabricated?
No. Metadata can be absent for legitimate technical reasons, so authenticity requires evaluation of additional evidence.
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