Csi Essay

When prosecutors present evidence to a court, they must be ready to show that the thing they offer is the same thing the police officers, crime scene investigators, and agents seized. When that evidence is not distinctive but fungible (whether little bags of cocaine, bullet shell casings, or electronic data), the "process or system" which authenticates the item is a hand-to-hand chain of accountability.

Although courts generally have allowed any witness with knowledge to authenticate a photograph without requiring the photographer to testify, that may not suffice for digital photos. Indeed, judges may now demand that the proponent of a digital picture be ready to establish a complete chain of custody--from the photographer to the person who produced the printout for trial. Even so, the printout itself may be a distinctive item when it bears the authenticator's initials, or some other recognizable mark. If the photographer takes a picture, and then immediately prints and initials the image that becomes an exhibit, the chain of custody is just that simple. But if the exhibit was made by another person or at a later time, the proponent should be ready to show where the data has been stored and how it was protected from alteration.

Technology is rapidly changing every aspect of the criminal justice system as computers make possible the streamlining of many procedures, shortening their time span and increasing their accuracy. Techniques used in the collection, processing and storage of evidence benefit from these recent developments.

Digital imaging, once used primarily for fingerprint comparisons, now is being used effectively in an increasing variety of evidence procedures, including analysis of altered documents, recording crime scenes and traffic crash sites, documenting domestic violence cases and creating video mug shot systems. However, as the use of digital cameras and digital imaging increases as a powerful crime-fighting tool so do the inevitable challenges to its admissibility in court. Therefore it's imperative that a prosecutor be familiar with the process and aware of preventative measures to overcome any objections at trial.

Digital images are pictures processed through a computer. The images can be created several ways. The most obvious way is with a digital camera which creates images that are eventually downloaded and stored on a computer. Another popular way is to scan a photograph directly into a computer. Scanning convert's original film photographs into digital images which can be stored, e-mailed, or enhanced. To get a better understanding of digital images and digital cameras, one must first grasp a few basic terms and procedures.

Computers understand and read coded numbers. In order for a computer to process pictures, the information must be converted to a series of numbers or digits, hence the name "digital".

These number sequences consist of bits and bytes that the computer reads a binary digit (bit) is the smallest unit of information a computer can process. Its value is always "0" or "1" which the computer reads as an on/off electrical sequence. Eight bits make a byte. A picture element (pixel) is a code consisting of bits of information representing a specific color, intensity and location. Pictures are made up of many different pixels. This digital representation of a photograph is stored in the computer on a rectangular grid called a bitmap. The more pixels per Inch (ppi), the sharper and clearer the final photograph will appear.

To acquire photographs, a digital camera uses the same principles as traditional film. Instead of using light-sensitive film to record images, most digital cameras use a light-sensitive chip called a charged coupled device (CCD) to record the image electronically. This is the same image sensor used in most video cameras. The light sensors on the CCD capture and store the image as red, green, and blue pixels. The electrical output of the CCD is sent to a converter which changes the image to a digital output. The data is then computer to process pictures, the information must be converted to a series of numbers or digits, hence the name "digital". These number sequences consist of bits and bytes that the computer reads.

The electrical output of the CCD is sent to a converter which changes the image to a digital output. The data is then stored in the camera as a computer data file with each file representing a different photograph. Some digital cameras have the ability to display the resulting images on a view screen; others require a computer to view the images. (The enhanced digital imaging process evolved from the NASA space program over twenty years ago. The technology was developed by the jet propulsion laboratories to isolate galaxies and receive signals from satellites in the late 1960's.) After a file is downloaded or scanned into a computer, an image can be enlarged or enhanced by using one of several software programs available. By using software, poor quality or obscured details in photographs can be enhanced in an attempt to bring out fine points that are not visible to the unaided eye. (Miller, Larry S.)

In explaining this process, it is important to distinguish between enhancement and manipulation. The software enhances photographs by improving sharpness and image contrast; nothing is added to the image. It makes what is there more usable. Enhanced pictures are not changed or cut and pasted to create new images.

For example, pattern and color isolation filters can contribute to the enhancement process by removing interfering colors and background patterns. In this context, enhancement is comparable to adjusting a television's picture or tuning into a radio station.

Manipulation, on the other hand, is defined as "to change by artful or unfair means so as to serve one's purpose." Certainly, one could manipulate an image to create a fraudulent portrayal of a scene. For example, a segment of one picture could be cut and pasted into another picture creating a false representation. However, manipulation did not originate with digital images. Some form of manipulation can be done with any generated piece of evidence to include videotapes, negatives, sound recordings, or traditional photographs. Where there is a will, there is a way. (Miller, Larry S)

Technology is catching up to the possibilities of manipulation in digital imaging. Currently, there are several software packages and digital cameras available on the market preventing the user from adding to, changing or destroying the original image. The original files are saved as a special type of file format that makes it impossible for the user to alter the original file in any form. An original picture must be saved as