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Next-generation surveillance system design

2/11/2008 08:00 AM EST
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re: Next-generation surveillance system design
jimhoerricks   4/1/2008 4:23:28 PM
A very well stated overview of your product with one very important omission - video surveillance systems as generators of evidence that can end up in court. If the purpose of your system is to monitor an area, without recording - then the system as described would work great. It's when the record button is pressed and a crime is "witnessed" by one of these systems that confusion begins. It all starts with the designer of the system. What is the system's purpose? Is it observation or monitoring of an area? Is to help in the recognition that some activity is occurring within an area? Is it there to aid in the identification of individuals and objects for internal purposes? With these questions in mind, will these recordings ever be turned over to the police? Each of the above questions will yield a slightly different system design. You simply will not be able to identify someone/something at a range of 250m with a 4.5mm lens. You will have difficulty identifying someone at 100' at 1CIF. But you can observe activity at these resolutions and distances. The state where the installation takes place will have it's own evidence code, governing statutes, and case law. These all need to be taken into consideration when designing a system and selection a codec where the data will be used to prosecute offenders. There is an interesting trend in the courts where MPEG4 based video is becoming more of a problem in a prosecutor's case than a help. Here's a question: Can a "B" or "P" frame be considered a "true and accurate representation of a scene?" Many states, and the Federal Rules of Evidence, have specific guidance as to how this "true and accurate" clause is to be interpreted. If the B and P frames are only representations of the change that the computer predicts between I frames, then how could they be considered "true and accurate" under the rules of evidence - thus summarizing the defense's objection to the evidence as such? With that in mind, how frequent are I frames generated? 1 second? 5 seconds? It varies by manufacturer and by installation. How reliable are the rates in practice vs. what is published by the manufacturer? In one famous case in Florida, there was such a variance that the prosecutor could not use the video - prompting the dropping of charges and a counter suit for false imprisonment. Hopefully, some consideration will be given for the fundamental change that occurs when the "record button" is pressed - for the potential problems that exist when multimedia data becomes multimedia evidence. Jim Hoerricks Forensic Image Analyst

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