Published August 11, 2017
Here in 2017 you’d think the last thing we’d be talking about is a revolution in forensic biometrics. But I believe that is exactly what is needed.
For the best part of three decades we have been committed to live scan technology to acquire fingerprints and palm prints from known individuals, and for three decades we’ve been apologists for the limitations of these records.
The limitations of these process are well known. I’ll touch on a few issues below.
We know the most significant issue with live scan records are the artifacts (false level two features) that can be created during the image acquisition process. These artifacts differ somewhat from the artifacts we used to create with ink and paper because the smudging and tonal shifts that helped us identify and resolve these artifacts is removed by image enhancement processes in the live scan software. This is done to make the final image more visually appealing.
Friction ridge artifacts are created during the transition between the three-dimensional object (the hand or fingers) and a two-dimensional surface. These artifacts usually appear near the tips but not always. They can occur where you least expect them, and when they do, they can easily lead to a false negative evaluation, especially if the latent is not robust.
We also know of several other problems with certain live scan systems. These include issues such as feathering, ghosting, stitching, and over exaggerated friction ridge deviation. Perhaps the most surprising limitation is, that because of the method used in acquiring images we only end up with half of the friction ridge detail available on the fingers and thumbs. This is due to a technique known as, “rock and roll”. The technique requires a gentle rocking of the finger to activate the sensor. The technician then fills the screen as best as they can, to capture the fingerprint. I have spent time observing this process in a lock-up and noticed that the fingers and thumbs were only being rotated 45° in each direction. Conversely, when we acquired fingers and thumbs using the ink and paper method, we rolled the prints from nail edge to nail edge. Or 90° each way. The additional 45° degrees x2 of information becomes extremely valuable in resolving ordinary latent prints from things like beer bottles and cans where we typically see the very edge of index fingerprints and thumbprints.
So, what is the solution?
I believe the solution can be found by moving away from two dimensional known records. We need to create known records in three dimensions. Hands and digits are three dimensional objects and should be recorded in three dimensions. The impressions they create are two dimensional (most of the time). I’m certain, in the computer age that we can render a three-dimensional object into a two-dimensional image, we’ve done it with maps for years. We can use the computer to render the portion of the friction skin we need to resolve the latent print, while maintaining the integrity of the known record.
By capturing hands in three dimensions we will have access to all the friction ridge detail available. We will eliminate artifacting. We will capture all friction ridge detail including the detail sometimes not acquired due to deposition pressure or natural physical depressions. We will capture all the friction ridge detail from nail edge to nail edge including tips. We will capture the friction ridge detail on the phalangeal joints often unrecorded in flat impressions. We will acquire all the friction ridge detail in three dimensions including detail in the furrows that is sometimes not captured unless enough deposition pressure is applied. This becomes very relevant when comparing photos or videos of hands and fingers.
By adapting to using three-dimensional imaging of known hands we will maximize the opportunities to resolve almost all the very important latent finger and palm print evidence collected by our law enforcement professionals.