Dangers of Deleting Surveillance Video
In this update, we examine the risks of deleted surveillance video and best practices / settings to minimize this problem.
Fairly regularly, a news story emerges about surveillance video of a criminal incident mysteriously disappearing. In March 2010, surveillance video went missing [link no longer available] of an American football star accused of rape. In April 2010, the University of Maryland reported that surveillance video of a civil disturbance was lost. In the Mayland case, officials noted that the video automatically overwrites older video and that somehow a 2 minute gap appeared in the exported video.
While we cannot make meaningful observations on these specific cases, they are certainly consistent with a common problem in surveillance video use. Whether maliciously or by accident, surveillance video of important incidents can be lost.
How Recording / Deletion of Surveillance Video Works
By default almost all VMS systems automatically delete the oldest video stored (often called FIFO for first in, first out). In addition, most systems allow users to set the maximum storage duration of video at which older video will be discarded even if space remains (e.g., 30 days storage is set, video that is 31 days old is deleted even in 1TB of storage is 'free').
Most surveillance users tend to economize on the surveillance video - purchasing just enough for their needs. This is driven both by cost and also by the inflexibility of most systems to add more storage without deploying new appliances or changing the existing design.
Advanced Settings that can Impact Storage Duration and Deletion
Storage Duration by Camera: A number of systems have settings where you can adjust the maximum storage duration independently by camera. The advantage of this is greater flexibility to keep video from certain 'high risk' cameras longer than 'lower' risk. The downside is increased confusion or risk that someone forgets or allows video to be over-written (e.g., they did not realize that camera 3 is only set to 7 day storage but camera 4 is set to 14 days).
No System Level Access to Delete Video: Very rarely do VMS systems allow users to delete video from within the application. It's highly uncommon to find a 'delete video' button inside the client application. This provides some safeguard against accidental or malicious deletion.
Accessing Directory where Video is Stored: In most traditional appliances (e.g., DVRs), it was either not possible or very difficult to access the stored video files directly. This provided additional barriers against a malicious user from deleting video. However, most VMS systems by default, allow any user who can access the VMS server to go to the the folder(s) where video is stored and manually delete video with a click of the button. This is an especially important risk if you are concerned about an admin or technician having motivation to do so.
Locking Video / Removing from Deletion Queue: While exporting video is the most common way of ensuring that surveillance video is not lost, some VMS systems allow you to flag or mark video segments to prevent them from being deleted in the normal FIFO / oldest video cycle. One practical downside is that the implementation of this feature requires marking each camera and time frame individually so it can be cumbersome to simply set all video from a 1 day or 1 hour to be locked.
It's easy to say that video should be exported immediately or that more storage should be provided to keep video longer. In practice, both have their limits. People often forget, delay or do not know how to export. Plus, more storage tends to be costly and requires a procurement process.
The two less commonly used points we'd recommend are:
- Restrict Access/Rights from Stored Video Directories: Make sure that surveillance video cannot be easily manually deleted from the server it is stored. Implement restrictions on accessing these files. Downside is that it requires some IT expertise.
- Lock Video to Stop Deletion: As soon as you believe an incident might require investigation, lock the video to prevent automatic deletion. Downside is that many systems do not support this feature and it still requires an operator to know how to use the feature. Upside is that it can be done quicker and for broader time frames than exporting to file, CD or DVD.