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Handling video for use in court

Video surveillance is most powerful when getting an early conviction without going to court. Basically, when the police show the accused video of them in the act of the crime, they are likely to agree to a plea bargain for a lesser charge and avoid court entirely, saving time and tax money.

But that’s before court. What would a judge say about that same video?
Many attorneys claim that admitting video into a trial has both benefits and pitfalls that can help or hurt their case. Even if the video catches the accused in the act, it’s not always enough to get a conviction.

Compression in Court

Often when I discuss compression methods during training courses someone will state that only Motion JPEG compression is admitted in court. The argument for MJPEG is it’s the best video compression because every picture frame sent from the network camera is a full frame. They assume that since the picture is in one piece that this is better for admission in court. While some Canadian entities have standardized on MJPEG because of this feature, it’s still not law.

Others argue that not each and every frame is needed because video by definition is motion and the courts only need to see the video clip, not each frame. Other compressions, namely H.264 and MPEG-4, take an initial full snapshot and then only send the changes in the image in subsequent frames until it produces another full frame shot.  MPEG-4 and H.264 are often favoured in security because they can store video for a longer period of time — meaning more evidence could be found.

Interestingly, each of these compression methods have been accepted in court and each have been rejected in court. So how do you determine if your video is court-approved?

Defeating the Defence

The most important consideration for any piece of court-approved evidence — including video — is its chain of custody.  The FBI has put together six criteria for video evidence being admitted into court that follow chain of custody guidelines:

Who captured the image and when?
Who had access to the image between the time it was captured and the time it was introduced in court?
Has the original image been altered in any way since it was captured?
Who enhanced the image and when?
What was done to enhance the image and is it repeatable?
Has the enhanced image been altered in any way since it was first enhanced?

A defence attorney’s job is to defeat any of these six criteria in order to cast doubt on the authenticity of the video. For example, if someone took the original video and enhanced it, that would violate the chain of custody because the original video is now permanently lost. At a minimum you need to store the video somewhere in its original form for the duration of the trial. Any enhancements must be done on a copy of the original.

Unfortunately for prosecutors, TV shows like CSI and Law & Order have raised the stakes on what jurors are expecting when shown video evidence in court. These popular shows have viewers believing that a video taken at the scene of the crime can be endlessly analyzed and enhanced to get the proper results.  Maybe someday cameras and analytics will be able to get fingerprint details off a piece of glass or see a facial reflection off a window and compare those to the RCMP database for quick arrests — but that day is very far off.

Today the ability to do further forensics on your video mostly comes down to starting out with high resolution images. A popular industry standard today is HDTV 1080p network cameras, meaning you get quality images based on the same SMPTE HDTV standard used in the entertainment industry — something everyone sitting on a jury can relate to. With these higher resolution images you can zoom in on the frame shots after-the-fact and pick up additional detail. 

Pixel Proof

But how much pixel detail do you need to solve a case?  Unfortunately for those who like cut-and-dry rules, only a few countries in the world have developed court-approve standards for pixels in an image. Canada is not one of them.

If you look at common internationally adopted standards, the courts call for 80 pixels per foot to accurately identify a person and 15 pixels per license plate height for license plate recognition.

Examples of different pixel per foot scenarios when identifying a face. Note that Canada is not one of the countries that currently outlines court-approved regulations for numbers of pixels needed for identification.
It is a mathematical formula to determine if you have enough pixels on target. Taking the 1080p resolution example, there will be 1920 pixels on the horizon.  Therefore, the maximum horizontal field of view that meets the 80 pixel target is 24 feet.  In other words, if you are setting up cameras for a bank teller area and the counter is 90 feet long, you will need a minimum of four cameras to get the correct coverage to have enough pixels for solid identity detection.

Technology is moving so fast that it is continually ahead of the court system. But fortunately, no matter how innovative your security technology, the chain of custody is there as the ultimate guideline. Utilizing this and some basic principles you can be assured the video will pass the admissibility test in court.

Robert Moore is Canadian Country Manager, Axis Communications. Robert.Moore@axis.com