The modern mugshot, with a frontal and profile image apiece, was devised by the famous French criminalist Alphonse Bertillon in the late 19th century. For more than a century, it has provided law enforcement with a way to catalog and keep track of repeat offenders and suspects.
The problem: it is inherently two-dimensional, and doesn’t readily allow for comparison with images that may be important to an investigation, such as surveillance camera footage from a high angle at a crime scene.
But now there is a new photogrammetric system which creates a 3D composite for investigators to use as an identification comparison reference, as presented in the journal Forensic Science International.
“We have developed a fast 3D mug shot system for the documentation of human faces,” write the Swiss authors, from the Zurich Forensic Science Institute and the University of Zurich. “The documentation itself only takes a split second. The system also includes the standard 2D mug shots.”
The photo-taking arrangement is elaborate. Twenty-six digital single-lens reflex cameras are arranged in a semi-circle of a 200-degree arc, at a 1.46-meter radius, around a height-adjustable chair.
Twenty-three of the cameras are used for the photogrammetry, which resulted in building a texture of 8192 by 8192 pixels, according to the paper. Three difference focal lengths were used: 50 mm, 85 mm and 135 mm.
The photogrammetric data were processed into a true-to-scale 3D model using Agisoft PhotoScan Professional.
Using so many cameras means the subjects do not have to sit still for long periods of time, according to the study.
“Multi-camera systems are a fast 3D documentation method, which overcomes (timing issues) due to their swift scanning procedure and therefore is often used for real-time 3D documentation,” write the authors.
The 3D distinctions were made down to minute details: for instance, the nose alone included calculations of the bridge, tips, septum, nostrils, nasal wings and alar groove.
Comparisons of the 3D photogrammetry were made with data from two light scanners: the GOM Atos Triple Scan (Germany) and the Artec Space Spider (Luxembourg). Also included in comparisons were high-quality 2D digital images.
Limitations included: some shadows that were caused by light coming from a window where the 3D images were captured; and also ear features, which were less well capture, partly perhaps because of the light situation.
But the new 3D system allows for much more all-encompassing comparisons, without requiring a suspect to sit for a laser-scanning “portrait” that could take up to five minutes, according to the authors. The new system could thus be a game-changer for getting better comparisons from visual evidence.
“The major advantage of the system is that the generated facial 3D models can be adjusted in head orientation to the perspective captured on the comparative surveillance footage, thus improving the conditions for image comparisons between the mug shot and the person of interest,” they write. “The 3D mug shot system, may be used as a complementary tool along with the traditional 2D mug shots for the purpose of visual forensic identification.”