What the police want in a CCTV system to use as evidence in Australia

Jun 7, 2020
Face Identification (120%)
(480 Lines over height of person)
Face Recognition (50%)
(200 Lines over height of person)
Intrusion Detection (10%)
(40 Lines over height of person)
Crowd Control (5%)
(Monitoring)
(20 Lines over height of person)
Figure 1. Comparative representation of the four police recommended resolution levels.
* Note: Digital image equivalents created using a Kell factor of 0.76.
1. The percentages refer to the minimum quantity of individually resolvable lines required over the height of a person, in relation to an industry standard of 400
Lines. For example, to achieve Recognition (50%) resolution, the system must be able to resolve 200 lines over the height of a person (i.e. 50% of 400 lines).
This does not mean that the camera view needs to cover the entire person, or that a minimum of 200 or 400 lines is necessary! Continuing the example, if the
person is 1.6m tall, to achieve Recognition (50%) resolution, the CCTV system must simply be able to resolve individual lines down to 8 mm wide at the target
location (1.6m divided by 200). Recognition (50%) resolution (i.e. 8 mm wide lines) is indicated by line A on the accompanying Test ChartIntroduction

Many people are not aware that there are specific rules and guidelines on exactly what the Police require when it comes to CCTV installations and the quality of recording.

This was written for businesses, however the same principles apply for home security.

Face vs crowd

When considering your system, you will need cameras that capture the overview or the crowd, and cameras that capture the face. Generally these are not the same camera as the wide angle cameras are great for capturing the event or crowd, whereas narrower cameras with a greater zoom (aimed at entrances) will capture the face.

The image above from the Police document showing what happens to faces when the image is zoomed and what the police require. You will see that wide angle shots are almost useless when you zoom into the face, and zoomed images are useless when seeing the overall event.

Some of the key Police recommendations

Apart from the most important area discussed above which is a. getting the culprits identification and b. seeing the overall actions, there are quite a few other areas discussed in the downloadable report below.

Here are what we consider to be the key areas.

  1. Ensure your system holds 31 days or more
  2. Ensure you do not reduce quality or frame rates to a point it affects quality
  3. Ensure your compression algorithm does not deteriorate the image quality
  4. Ensure your system restarts into recording mode after power cut
  5. Overlap cameras to avoid gaps
  6. Ensure a high enough frame rate to avoid missing sections
  7. Have some eye level cameras
  8. Avoid back lit areas
  9. Have cameras zoomed to entries and exits for facial shots
  10. Have car park cameras zoomed to entries and exits for number plates
  11. Have both wide shots and identification shots
  12. Keep your system secure
  13. Avoid weather affected camera locations
  14. Regular testing and maintenance