How to Provide Usable Evidence that Stands Up in Court
There are two main aspects of data provenance –
1. Ownership of the recording: Ownership tells the court who is responsible for the source of the data, including information on the originator of the recording.
2. Recording usage: This gives details regarding how the recording has been used and modified and often includes information on how to cite the data source or sources. Recording provenance is of particular concern with electronic data, as data sets are often modified and copied without proper citation or acknowledgement of the originating data set.
Thus, images destined for use in a court of law must be obtained and processed using carefully documented procedures if they are to be allowed as evidence. The documentation typically includes the name of the photographer, the date the image was obtained, the names of anyone who had access to the image before it was introduced in court, the names of anyone who enhanced or altered the image, whether the alteration was performed on the original file or a copy, and the details of any enhancement procedures.
When all is said and done, there are three variables in providing the type of recordings that the courts want –
1. Encryption: To safeguard the validity of recordings as evidence, information assurance measures must be taken to prevent the video data from being tampered with or altered. Thus, video encryption of recorded images is necessary for court admissibility purposes.
Digital watermarkingembeds information into a digital signal which may be used to verify its authenticity or the identity of its owners, in the same manner as paper bearing a watermark for visible identification. In digital watermarking, the signal may be audio, pictures or video. If the signal is copied, then the information also is carried in the copy. A signal may carry several different watermarks at the same time.
To assure that the recording has not been tampered with, courts will prefer using a fragile digital watermark. Fragile watermarks fail to be detectable even after the slightest modification. Thus, if the watermark is visible, the recording has undergone no tampering. That proves provenance.
2. Frames per second: Frame rates affect storage. Full-motion video at 30 fps is seldom used because less may be sufficient. Many times, administrators adjust frames per second for each camera based on its location and scenes.
In a gaming application, for instance, a casino camera would be 30 fps, as opposed to a backroom operations camera, which would record at 15 fps or lower.
The table here shows how quickly frame rates can yield big storage challenges.
|Image Size (in kb)||Frames per second||Mb per hour|
The concern is that a slower frame rate may or may not catch what actually happened, although it probably will. Thus, to conserve bandwidth and storage, some systems record only a frame every two or more seconds. Such slow frame rate is sure to miss something.
In many cases, operators can have their cake and eat it too. They can record at a low frame rate when nothing is happening, but when motion detection or an alarmed event occurs, recording switches to a high resolution and maximum frame rate.
3. Resolution: In a court of law, one needs good resolution. Being able to see the perpetrator clearly is imperative in order for the jury to be absolutely certain beyond reasonable doubt that the defendant is the person shown in the video.
However, keep in mind that when a suspected person is shown a low-to-medium resolution picture of them committing a crime, they almost always confess and plead guilty. But a suspect with money can hire a "good" attorney who will deny it was his client and force a jury to decide. So, provide the highest resolution that you can afford. Yet, in attempting to ensure clear images, new challenges arise.
For instance, if analog cameras are coexisting with a digital recording system, there could be noise. If so, it will generate additional storage requirements. And, even though a 5 MP camera always generates 5 MP of storage, the value of the images can vary. However, very few applications will require 5 MP. In most cases, 2-3 MP is needed, although the 1.3 MP version remains the workhorse of IP cameras.
The balance between encryption, frames per second and resolution can be delicate is assuring that images will meet court requirements.