Forensic Fingerprint Imaging

Automated Photography and Enhancement of Fingerprints on Cylindrical, Curved and Highly Reflecting Evidence

The photographic documentation of visible or chemically enhanced fingerprints on the surface of cylindrical, curved or reflective evidence is associated with a number of difficulties and therefore often involves a considerable effort.

Cylindrical evidence, such as bullet casings, drinking glasses, bottles, ampoules, cans, etc., pose a particular challenge as the depth of field in a photographic image decreases with increasing magnification. Therefore, the conversion of a curved surface into a two-dimensional “photographic” image inevitably results in a geometrically incorrect photo.

With conventional photographic methods, such finger-print or trace images can only be recorded in several sections and with geometric errors. The analysis and comparison of individual characteristic in several images is therefore not an optimal basis for the subsequent dactyloscopic evaluation of a fingerprint.

Finger or grip marks that extend over a larger section on the outside of a cylinder can naturally not be visualised when viewed frontally because a part of the handprint on a circular surface facing away from the observer is hidden by the evidence item itself.

Structure and Major System Components

A special OLED line light with a natural colour spectrum is available for illuminating the capturing area on the surface of the evidence. The possibility of illuminating the surface of an object in a linear form in compliance with the recording method opens up completely new areas of application for forensic fingerprint photography.

Interfering reflections, shadows or poorly illuminated areas on the surface of cylindrical or transparent evidence items are effectively eliminated by the linear scanning mode in combination with a “line-shaped” illumination.

On the other hand, by capturing an image directly in the reflective plane or directly besides an illuminated column, it is possible to photograph fingerprints on mirrors and other highly reflective surfaces without generating disruptive double reflections.

Independently of the built-in line light, the open design of the ForensiScan allows the application of various other types of lamps, e.g. special forensic light sources. These other light sources can be flexibly positioned around the evidence area and applied for optimal illumination of the evidence under examination.

System Components and Accessories

The ForensiScan is equipped with a high resolution RGB camera and a motorised lens.

All camera parameters (focus, aperture, resolution, gain) are set digitally via the user software. To simplify focus adjustment, the software has an integrated autofocus function and the option of “focus peaking”.

The position of the camera in relation to the evidence object can be precisely adjusted with the help of fine mechanical gears. Roll angle and tilt of the camera can be adjusted with micrometer screws.

Optionally, the camera can be supplied with an extended spectral range for images in the near infrared range (up to 950 nm).

ForensiScan – Technical Specifications

Dimensions

110 cm x 78 cm x 80 cm

Weight

approx. 20 kg

Maximum resolution (vertical x horizontal)

Rotary mode: 4,096 x 72,000 Px (294 MPx)
Linear mode: 4,096 x 80,000 Px (326 MPx)

Camera and lens

RGB camera
Resolution: 4096 x 3000 px RGB F = 45 mm
Lens mount: MFT interchangeable lens
Max. distance to rotation axis: 0 mm - 500 mm Max. height above turntable: 450 mm
Vertical angle of view: 15.8° (roll angle adjustable)

Turntable

Internal reference angle
Maximum object size: 500 mm x 500 mm Angular resolution: 0.005°
Load capacity: 20 kg

Turntable

Surface: aluminium, black Diameter: 300 mm
With concentric centring circles
Black plastic disc for height adjustment (“Puck”)

Clamping device

Designed as triple jaw chuck Colour: black
Object diameter 0 mm - 120 mm Optional Additional positioning aids on request

Centring aid

universal centring tip with different design options Height adjustable
Contact pressure variably adjustable

Linear unit

Internal reference position Quick-change adapter Linear resolution: 0.005 mm Maximum distance: 40 cm