DIGITAL CAMERA CONSIDERATIONS
FOR CRIME SCENE INVESTIGATIONS

1. Elements of Camera Selection

A. CCD Sensor - Density and Resolution

The CCD Sensor (Charged Coupled Device) is the device that substitutes for film in a traditional camera. It is typically composed of hundreds of thousands of elements called PIXELS (Picture Elements). If you think of looking through a window screen, each pixel corresponds to one "hole" in the screen. Another way of thinking about pixels is traditional "film grain" -- the coarser the grain, the less detail can be captured.

Digital Cameras today have CCDs composed of hundreds of thousands of pixels or even millions of pixels; generally the more pixels equate to a better quality final image. This generally is referred to as CCD Density.

Full color photographs require combinations of three colors: Red, Green and Blue (RGB). Today's CCD sensor is therefore "striped" or "masked" with tiny Red, Green or Blue filters on individual pixels. The digital camera then analyzes the mosaic color pattern and computes all of the colors for a true color image. In other words, the photograph is based upon computer analysis of red, green and blue pixels to create the final image. Therefore, two, three or more pixels are analyzed to determine the actual true color of a particular point in the picture.

The final picture is stored in digital format with some number of full color pixels defining the image. This is defined as image "resolution" . Inexpensive cameras produce a final picture of 200 x 320 pixel resolution, more expensive cameras have much higher resolution, typically 1280 x 1000 or more.

The better quality cameras will produce a high resolution file, typically at least 3mb in size. But beware of "interpolation" (see below)!

B. CCD Quality

There is a significant difference in the image quality produced by various manufacturers. In general, more expensive digital cameras have higher quality sensors, therefore better picture quality. An indication of inexpensive sensors is "noise" in the pictures -- much like "snow" that you see on your TV. Look especially in the shadow (dark) areas of your picture. Cheap sensors result in grainy, snowy images and resultant loss of details and overall picture quality.

C. Lenses and Lens Capabilities

Consider the special needs of forensic and crime scene photography. Inexpensive digital cameras, like inexpensive film cameras, have fixed plastic lenses that can compromise picture quality. More expensive cameras have telephoto, macro (close-up) and even interchangeable standard camera lenses. Consider the typical crime scene -- you will probably need wide angle, close-up and macro photographs.

D. Data Interpolation

Some digital cameras produce a "native" file -- one that the full color image file is determined solely by the number of pixels on the CCD sensor. However, some digital cameras enlarge the file size by "interpolation" or computer processing. The interpolated file size is indeed larger, but the picture quality is NOT improved, and is of less quality than a comparable "native" file size.

For example, you can watch a television program on a 17" TV or a 60 "TV. Although the picture is larger on the 60" TV, it shows no more detail -- it’s simply larger.

Beware of digital cameras that interpolate file size. This often means that the sensors are inexpensive, low density CCDs, but they want you to think you are getting high quality file sizes.

The point is, if the final file size is the same, a native image file will always be superior to an interpolated file. So, do not just read the sales brochure, inquire about interpolation.

E. Storage Media

All digital cameras that should be considered for crime scene photography use removable "memory" or digital cards (PCMCIA Cards or "PC Cards". These cards come in essentially two flavors: Type II (1/8 inch thick) that are made of computer memory; and Type III (3/8 inch thick) that is actually a "mini-hard disk" that works exactly like a hard drive in your computer.

The digital crime scene camera will be used in the field. PCMCIA cards will be transported, inserted and removed from cameras. It is inevitable that a card will occasionally be dropped. A Type II card is 100% solid state, and therefore fairly rugged -- and can be accidentally dropped without damage.

If you would take your hard drive out of your own computer and drop it on a concrete floor -- help yourself to a Type III card. The results on both will be the same. Not only will you lose your hard drive and Type III card, but the data as well. No more crime scene photographs!

BEWARE OF ANY DIGITAL CAMERA THAT USES A TYPE III (HARD DRIVE) CARD!! ASK YOUR SALES REP IF HE WOULD MIND IF YOU DROPPED HIS TYPE III CARD ON A NICE HARDWOOD FLOOR! WATCH CLOSELY HIS REACTION.

F. Camera Features

You get what you pay for. All digital cameras will operate in an "automatic" mode, setting shutter speed, aperture, flash and focus. More advanced cameras will let a crime scene photographer adjust those settings for current conditions. You should determine what features are important to you.

Some advanced cameras permit audio recording through to be attached to each photograph. Investigative comments can be attached to each photograph. Some cameras even permit a GPS (Global Positioning Satellite) receiver to be attached, and it files the exact latitude and longitude location on each picture. Nice for field operations.

Other camera features may be available. The user should consider carefully the applicability of these features for crime scenes.

G. Preview mode

An extremely useful feature of many digital cameras allows the technician to review each picture on a small color display. Using this feature, each picture can be reviewed at the crime scene to check for focus, composition, detail, lighting and other quality issues. If additional pictures are required, they can be taken immediately, PRIOR TO THE RELEASE AND CLEANUP OF THE SCENE.

We have all heard of instances where film photographs were taken of a scene, and the photos turned out all black because of mishandling or ruined film at the lab. This possibility is virtually eliminated by reviewing the pictures prior to leaving the scene. If you have one or two bad pictures, simply retake them!

H. Digital Card Picture Capacity

Digital Type II PCMCIA cards come in varying sizes and capacities from 2mb to 40mb. The larger capacity cards will obviously store more pictures; but also are more expensive to purchase. We generally recommend against purchasing the largest capacity cards for two reasons. First, the cards are more expensive. Second, if a card is lost or damaged, not only does the jurisdiction suffer the dollar loss of an expensive card, but potentially a large number of photographs are lost as well.

We therefore recommend that a user purchase several lower capacity cards and carry several to the crime scene. Thus, if a card is lost or damaged, the dollar cost is smaller and there are still photographs on the remaining cards.

I. Ultraviolet lighting

We have had good success in capturing ultraviolet photographs of semen or other fluids using digital cameras. The user is cautioned, however, that some manufacturers provide UV coating on their lenses that may affect this application. If this is an important use for your jurisdiction, thorough testing is recommended before purchase.

J. Digital File Formats

There are many industry standard file formats that are used to store picture information. Standard formats include .BMP, .gif, .TIF, .jpg and others. Unfortunately, some camera manufacturers have chosen to implement their own proprietary format for recording the picture. This requires the user to view the pictures only through THEIR proprietary software, and then convert it to industry standards for use, for instance with Adobe PhotoShop software. We consider this to be a significant pain, especially as there is NO advantage to the user -- only to the manufacturer who wants to lock you into using their software. Our advice: avoid proprietary formats.

K. Focal Length and Viewfinder Implications

Some digital cameras, particularly those with interchangeable lenses mess with the focal length of the lens. Many cameras actually "double" the focal length, making a 35mm lens act like a 70mm lens. This may be unacceptable in many crime scene applications, as it does not permit the technician to photograph a full room scene because of the telephoto effect. Even if a 20mm or 24mm lens is available, this doubling still effects a 40mm to 48mm focal length -- still too long for many applications.

Other manufacturers have reduced the "active" area of the viewfinder. In this case, even though the photographer sees the full viewfinder scene, the picture will only be a small portion of the viewfinder. This imposes conditions under which the photographer must operate. Extreme care must be taken to compose the photograph within the "active" area of the viewfinder, or the resulting picture will be unacceptably cropped.

L. Battery Power

Believe it or not, some manufacturers have used non-removable rechargeable batteries. What happens when the battery runs out at a crime scene? The camera also has to be returned for several days to a Service Center when the battery completely fails (will crime cease when your camera is out of service?). Would you buy a communications radio that had a cemented-in battery? Of course not. Be CERTAIN to buy a camera with replaceable batteries (that YOU can replace at a crime scene) and buy a few extra to keep charged in the camera kit.

M. Limitations of Digital Cameras

The current state of the art permits a digital camera and proper printer to produce an 8x10 color photograph that is virtually indistinguishable from a traditional film/chemical based photograph. However, there are some limitations that the user must consider:

a. Painting with light -- currently multiple exposures of the same image, commonly referred to as "painting with light", is not available on any digital camera that we are aware of.

b. Image Quality -- under most circumstances, digital photographs will be "as good" as traditional photography. However, there may be conditions where film based cameras will do a superior job. Such conditions may include low light scenes where flash is not desirable, very long lens surveillance, infrared photography or other specialized applications. In substance, if you implement digital, do not throw out your existing cameras. Remember that digital is a very useful tool, but you should maintain other tools including film as well.

c. Lens Choices -- for those cameras that permit interchangeable lenses, not all lenses will work effectively. If you have special purpose lens requirements, check it out, not all Nikon, Canon or Minolta lens will operate.

d. Digital cameras are all electronic. They may not be as robust in the rain or very damp conditions.

2. A Crime Scene Digital Camera Kit

1. Several Moderate size PCMCIA Type II cards

2. Native (non-interpolated) file size at least 3mb

3. Industry standard file format (typically JPEG)

4. Zoom lens (35-105mm is very desirable)

5. Preview capability to see pictures on site

6. Macro lens for close-ups

7. Extra batteries

8. Fully automatic mode, with manual settings for the experienced photographer

9. Acceptable pricing

10. A hard shell carrying case for camera and all other required items, including flash, PC cards, batteries, charger, measuring tape, scales, etc.

11. Full viewfinder framing

3. Advantages of Digital Crime Scene Photography

1. Ongoing Cost -- a one-time purchase of a digital camera and related equipment will eliminate (or very substantially reduce) the film and developing costs incurred by the jurisdiction. Look in your budget for the amount of money you spend in 35mm film and developing last year. You will be amazed!

2. Immediate Results -- there is no waiting for development of film.

3. Chain of Evidence -- many jurisdictions use commercial photo labs for developing and processing film. This by definition breaks the chain of custody and opens up possible challenges downstream. Because digital photographs are taken, stored and printed by authorized law enforcement personnel, the custody issue is strong.

4. Transportability of the Images -- any photograph is immediately available for transmission throughout the department or to other jurisdictions. Photographs can even be sent via the Internet to other appropriate parties.

5. Filing and Database Implications -- because the photographs are in digital form, they can be stored in a crime scene database on a standard PC for investigational purposes. Any authorized person could then review the photos via a standard PC network. Manual filing is eliminated. Have you ever looked for photographs, only to find out they were on someone else's desk? Or lost? Or misfiled? Never again with digital.

4. Summary and Disclaimer

Digital cameras are becoming increasingly affordable and useable in the crime scene environment. While they may have some minor disadvantages, we are of the opinion that they offer significant advantages to the law enforcement community. The information contained in this White Paper express the opinions of the author only, and should be read as opinions and comments only. The author believes all information contained herein is accurate, but disclaims any and all potential liability. The author recognizes that various manufacturers will continually improve their models, and introduce new models. We will attempt to keep this white paper current with such developments.

Police Central, Inc. is an Atlanta-based supplier of Law Enforcement Imaging Software. Current uses of Police Central software include Crime Scene Photography, Crime Scene Image Database management, Mugshot Management, Warrant Tracking, Law Enforcement Staff Database and ID, Megan's Law Sex Offender Registration, and other related applications.

For further information, interested parties may contact Police Central at PoliceCentral.com or at our headquarters at 6145 Barfield Road, Suite 127, Atlanta, GA 30328. Our telephone number is 1.678.904.1654.

Watch this site for future Police Central White Papers on the following subjects:

• Digital Photography and Courtroom Admissibility Issues
• The Complete Law Enforcement Imaging System, PC and all
• . . . other suggestions welcome

If you have enjoyed this document, or find it useful, please let us know! Thanks for your interest!

Copyright 1998 by Police Central, Inc. All rights reserved.