Crime scene photography, also called forensic photography, has been around almost as long as the camera itself. Investigators quickly realized that such technology could freeze time -- creating a supposedly incontestable record of a crime scene, a piece of evidence or even a body.

Today, forensic photographs are essential for investigating and prosecuting a crime. Photographs help preserve not only the most fleeting evi­dence -- like the shape of a blood stain that will soon be mopped up -- but als­o the placement of items in a room and the relation of evidence to other objects. Such images can prove vital to investigators long after the crime scene is gone.

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.

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 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 distance to show its relation to furniture, a blood stain, or the rest of the room. Mid-range images establish the distance of the object from surrounding objects.

Finally, the photographer thoroughly documents evidence with close-up images. Close-ups include identifying marks like scars on a body or serial numbers on a bloodied piece of electronic equipment. A photographer often includes 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.

Of course, pictures are of no value unless they're in context. The photographer keeps a photo log that includes every relevant detail, the photo number, any filters applied, the time and date, the location, and a description of the object.