At first glance, forensic photography is merely highly skilled commercial photography focused on recording places, objects and people. When these things begin to include crime scenes, weapons, injuries and other macabre things left behind where something grisly happened, we should probably regard this through a different lens.
To understand the mechanisms of what happened, the relevance of objects related to an event, and therefore the fault of persons involved, needs to be recorded for further study by law enforcement officers, attorneys and eventually judges and juries.
The end results — and accompanying detailed photographs and videos — will eventually be used in a court of law and require a high degree of authenticity. This is usually provided by the photographer both through a chain of custody, both to prove that the evidence has not been tainted, lost, purloined or misused in some way, as well as by direct testimony to verify the images and provide context. This authentication will also be supplemented by testifying experts and officers of the court as they explain how the images tell the tale of what transpired on a fateful night (or day).
Forensic photography, then, is a matter of determining which shots will best tell the story, and then systematically gathering those images, which will range from overall scene views to detailed minute evidence. It requires a skilled forensic photographer with: the right tools; a good eye and an understanding of police protocol; a knack for evidence handling and authenticity (so he or she will be able to determine which images to capture); and the know-how to solve technical problems in order to capture those images, and protect them so they are useful.
Crime scene image gathering does offer some particular challenges that commercial photographers never encounter. The best forensic photographers have come up with techniques that solve those very challenges.
Challenge one: the unrepentant serial number
Serial numbers on mechanisms like weapons, vehicles, machinery, medical devices and other property sometimes can be worn, scratched, filed off or even painted over. But because these numbers are generally stamped into metal, the impressions are still there for one who has the insight to look deeper. One method of revealing ghost images of serial numbers requires a little finesse with powdered chalk.
First, remove any grease or debris from the area of the number (after first photographing it in its natural condition). When the area is completely dry, lightly dust it with chalk powder (white on a dark object, or black on a light object for contrast). Use an alcohol wipe straight across the surface to remove the excess dust which was not trapped in the depressions. Don’t scrub. The numbers will stand out in contrast, due to the chalk caught in the depressions. Using a close-up lens and a tripod, vary the lighting to enhance the numbers. A straight down studio light may not be quite as revealing as a light cast from the edge, which makes shadows that add depth and enhance the powdered numbers.
Challenge two: blood blowback
Blood spatter, blood drops, pools of blood — for a blood spatter expert, every drop, every patch of blood splashed on walls, furniture, floors and objects can tell a very revealing story. When the photographer is capturing all of the blood evidence, they should not fail to look for blowback or the blood spray that would splash away from a wound and attach to the weapon and the perpetrator. It is a scientific principle that blood will be sucked backwards in the vacuum left by a passing projectile, and sometimes it will be sucked into the bore of the gun itself.
Criminals may wipe a weapon clean (or so they think), but the clever use of a borescope and a 90 degree mirror tube can provide evidence of that spatter inside the gun barrel, which should be photographed and then collected before any other processing is done on the weapon. A caveat: test firing the weapon to get a bullet match will destroy that DNA evidence, so look before you fire. Obviously, look down the barrel only when the weapon has been unloaded and verified.
Challenge three: capturing ghost bruises
Not all bruises on a victim will be obvious to the naked eye, so when taking pictures of a victim’s body, assume that there is evidence hidden in plain sight. Once general photos are taken of cuts, bullet wounds and obvious injuries, quickly place a special UV filter (Kodak’s Wratten 18A – about $500 USD, which allows only a wave length of around 400 nano-meters of UV light) over the lens and look again. Long wave UV light penetrates deeper into the skin than ordinary light; therefore, bruises, bite marks and other festering wounds will become clearly obvious and able to be photographed.
Interestingly, tattoos, Mongolian spots and birthmarks go deeper into the skin than UV, so these will not show up. A bruise under a tattoo, therefore, will not be obscured by ink. The other challenge is figuring out where the invisible bruises are; since these bruises are not visible, a series of shots adjacent to each other (called ‘bracketing’) will ensure that the right spot is captured in at least one picture. And maybe something unexpected will show up in a neighbouring shot.
One more tip: be sure to explain that the images are from UV filter, and show natural light images of the same areas for comparison. One doesn’t want to be accused of doctoring evidence when simply photographing through a different light spectrum.
Challenge four: a technique from the psychedelic 60’s
Many organic fluids such as cleaned-up blood, semen, urine, saliva and other secretions are invisible when dry. But turn off the room lights, draw the shades and get out your ultraviolet light wand and you will be surprised at what jumps out. Bed sheets, bathrooms, or wherever people have interacted with each other in certain ways will leave traces that glow under the ‘black light’ UV projector. Even a bleached tile floor will glow with a tell-tale image pointing to exactly where blood was spilled. Photographing this evidence is simple, but requires a tripod and a long exposure (bracketing a few f-stops in either direction to be sure). Corroborate the same area with natural light shots as well for comparrison.
Challenge five: thinking like a bad guy
At the crime scene, of course, a checklist is critical in order to assure full coverage. After that task is complete, it is advisable for the experienced photographer to stop, look around, use what was just observed and think about what happened. By running a few possible scenarios in his mind, places where evidence could appear will become noticeable: cast off blood on the ceiling; minuscule dart-shaped dings in furniture from a ricochet; or subtle displacement of dust on a bureau where someone may have touched it when stumbling. Wadded-up candy wrappers on top of footprints might lead to fingerprints on a cabinet door where snacks are kept. These possible valuable clues will be long gone after the CSIs pack up and release the scene, so do take a moment to use the most important tool in evidence gathering — the brain.
Your Turn: Do you have any unusual tips for photographing obscure or hidden evidence? Seen any tricks on the CSI shows lately? Please tell us more – we’d love to hear from you.