How Crime Scene Photography Works

­Crime scene photographers must be methodical in their work.­ They can't afford to leave out an important piece of evidence or produce photographs that could be considered misleading in court. But they also have the press­ure of the entire operation behind them. Before other CSIs can touch or move any of the evidence and even before the medical examiner can remove the body, the forensic photographer must document the scene.

There are three classifications of forensic photos -- overviews, mid-range and close-ups.

If the crime took place inside, overviews include photos of the outside of the building, its entrances and exits as well as images that place the building in relation to its surroundings. Photos of spectators at the scene can later help locate witnesses or suspects. Overviews also include images of all rooms, taken from overhead and from each corner.

The forensic photographer then hones in on key pieces of evidence and captures images of them in the context. These mid-range photos might picture a piece of evidence, like a knife, but at enough of a distance to show its relation to furniture, a blood stain or the rest of the room. Mid-range images establish the distance of object from surrounding objects.

Finally, the photographer thoroughly documents evidence with close-up images. Close-ups include identifying marks like scars on a corpse or serial numbers on a bloodied piece of electronic equipment. A photographer will often include a ruler in the shot to establish scale but always takes a duplicate image without the measuring device. In court, the defense could claim the device covered something important.

And of course, pictures are of no value unless they're in context. A forensic photographer keeps a photo log that includes every relevant detail, the photo number, any filters applied, the time and date and the location and a description of the object. The advent of digital photography has helped to make some aspects of recording the time and date simpler and more verifiable.

­What does a forensic photographer need to document the scene? And what makes a photograph admissible in court? Find out next.

Early detectives used to sketch the scene of a crime. Photography introduced a way to produce images that were more true-to-life and credible than drawings. And while an honest and technically sound photograph can record the ori­ginal state of a crime scene, it's simple enough to manipulate a photograph or record an image that's drastically different from reality.

A good photograph of a crime scene must meet certain technical specifications: correct exposure, sharp focus and maximum depth of field, the portion of the photograph that appears sharp. The image must also be free from distortion. Such technical standards produce photos that will actually aid agents in their investigation of a crime.

But there are additional qualities that make a photo admissible in court. The image pictured cannot alter the scene or evidence -- say through strategic blocking with a measuring device or an intentionally shallow depth of field. The image must also be relevant to the case and should be composed with technical precision in mind, not emotional appeal.

Photographers might vary their kit based on personal preferences or the type of crime scene but most carry certain basics: a camera, obviously, and maybe even multiple cameras; filters; electronic flashes; various lenses for wide-angle, mid-range and close-up shots; a tripod; a measuring device; a gray card, which when combined with a light meter helps produce correctly exposed photographs; and a way to protect equipment from rain or extreme heat or cold.

Crime scene photographers usually use color images although black and white can be useful when documenting evidence that relies more on texture than color like latent fingerprints.

But do photographs of crime scenes serve any other purposes? Find out about a more artistic side of utilitarian images in the next section.

In 2001, police officers and artists uncovered a treasure trove in a city records warehouse. They found a stockpile of forensic photo negatives from the Los Angeles Police Department -- some dating back to the 1920s. The images include every-day crimes, as well as the most infamous murders and biggest busts in the city's history.

­Struck by many of the images' captivating, almost movie-like quality, the artists and officers launched an effort to preserve the negatives, some of which were beginning to decompose. They also launched an exhibition of the archive and sent it around the United States. A lieutenant who helped present the archive explained that the images' morbid artistic quality was a result of less-scrupulous forensics standards in times past. The photographers were sometimes willing to fiddle with a crime scene in order to produce the best shot. Consequently, the photos, though they still functioned as evidence, look more like art than modern crime scene shots.

However, art and crime scene photography have long been linked. The New York City freelance press photographer Weegee made a name for himself by capturing images of crime scenes, news sites and movie premiers with equal frankness and occasional irony. In 1941, he staged a solo exhibition at the Photo League in New York entitled "Weegee: Murder is my Business."

But it's not terribly surprising that people display a fascination with crime scene photography. The often grisly images are set in such normal locations -- the steak house, the parlor or the street -- and subsequently elicit a morbid curiosity. They're strangely like everyday life, yet entirely different and wholly unsettling.

To learn more about CSI, crime-scene clean-up and cameras, investigate the links on the next page. ­