IPfocus Don’t Be Guilty of Providing Law Enforcement
With the growth of video surveillance and the coexistence of analog and digital technologies in the transition to digital video surveillance, there are consequences involving storage, retrieval and image management. There are different uses and purposes of stored video, various locations where images can be stored, a myriad of storage types and business and operations issues to consider. This becomes a major challenge for recordings that will be used in the legal system. Author: Nathan Needel, Infinova Vice President, Sales-North America.
In trying to provide law enforcement with clear, concise images, few things can create data bits more rapidly than digital video or analog signals converted to digital information. In a typical surveillance project, there are several factors that affect the amount of storage including:
•Type of camera, analog or IP •Resolution, 1.3 megapixel, 3 megapixel, or others •CODEC, D1, HD720P, MPEG4, MJPEG, H.264, or others •Compression Ratio •Frame rate, 5 fps, 30 fps, or others •
Dual streaming, separate streams for viewing and recording
•Motion in the scene •Whether analytics is performed centrally or at the edge or both.
•Recording periods during the day •Levels of activity through the week
For instance, a system of 50 cameras undertaking six months of surveillance at 30 frames per second at 2.0 megapixel resolution running 24/7 at 100 percent motion will take up 869 terabytes (TB) of storage. With storage costing approximately $120 per TB, the cost of storing those images would be over $100,000!
Even highly compressed video involves data rates of millions of bits per second. Retrieval of video from storage is a key function and one that has grown more important thanks to the use of megapixel and high definition cameras which has spurred forensics applications in which more details allow security or law enforcement to see more of what happened. However, even though you recorded clear, crisp images showing a crime being committed does not mean the recording will stand up in court. How it was stored – the chain of evidence – can be challenged by the defense attorneys.
Provide Usable Evidence that Stands Up in Court There are two main aspects of data provenance, ownership of the recording and recording usage. Ownership tells the court who is responsible for the source of the data, including information on the originator of the recording. Recording usage gives details regarding how the recording as 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. Databases make it easy to select specific information from data sets and merge this data with other data sources without any documentation of how the data was obtained or how it was modified from the original data set or sets.
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
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anyone who enhanced or altered the image, whether the alteration was perform on the original file or a copy, and the details of any enhancement procedures.
One issue that is a particular concern when an image is obtained with a digital camera is originality. Whereas traditional photography produces a film negative or positive that cannot be easily replaced without detection, digital cameras produce electronic files that can be modified and overwritten either accidentally or deliberately. It is possible to open a file, make modifications, and then save it with the same file name even though the image has been altered. Computer systems used to store forensic digital imagery must therefore be secure enough to prevent accidental modification of or deliberate tampering with original files.
When all is said and done, there are three variables in providing the type of recordings that the courts want – encryption, frames per second and resolution.
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.
There are two types of data encryption: file encryption and full disk encryption. File encryption uses a key to encrypt individual files. It requires care by the user to ensure appropriate data is encrypted. Full disk encryption uses a key to encrypt all data on a drive. To users, it appears to be a standard drive and all files (temporary or regular) are encrypted. The user does not have to manage data. Thus, it is easy to use. Without the proper key, nobody can recover data from encrypted files or entire disk.
Watermarking. Digital watermarking embeds 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.
Effect of Frame Rates on Storage Requirements 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 below shows how quickly frame rates can yield big storage challenges.
Image size in Kb 15 15 15
Frames
per second 1
5 30 Mb
per hour 54
270 1,620
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.
Image Quality Also Affects Storage Needs Resolution is an important consideration. 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 the end user can afford. Yet, in attempting to insure 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. Working with an experienced, certified integrator is key. And, if you're not sure which integrator to use, hire a technical security consultant to develop formal bid documents which list the qualifications of the installing contractor.
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