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Cctv Analysis in Digital Forensics Picture the latest crime drama: in the modern, glass-partitioned lab the large wallmounted monitor lights up as the Technical Specialist pauses the video on a shot of the suspect’s face and zooms in. The monitor flickers as he keys in the instructions for the computer to enhance the image. The computer whirrs as previously blurry pixels become sharper and begin to form a more detailed, recognisable face. The computer then crossreferences this with its database of thousands of photos. It flashes through image after image, until it spots a match. As entertaining as this is, how does it compare to the reality of CCTV analysis? In reality, there is only so much that ‘enhancement’ of CCTV footage can achieve. Enhancement can only work with the pixels that already exist within the footage; it cannot add extra detail or pixels that are not already there, as is commonly portrayed in cop shows. What it can do however, is to improve aspects of the footage like the brightness, contrast or clarification. These can help to improve the clarity and quality of the CCTV footage, making details easier to view and potentially highlighting new, previously unseen information as well. There is a lot more intelligence available from CCTV analysis than just image enhancement and facial identification, which features prominently in the majority of cop dramas. CCTV analysis can also be used for clothing or object comparisons, height estimation, establishing the time of an offence, vehicle comparison, voice comparison, and even gait analysis, all of which can provide useful intelligence for a variety of matters. We were involved in a case where CCTV footage was being used to identify a suspect by his facial features. Unfortunately, the images were too low resolution to be used to identify the suspect. However, we used other information contained within the footage to achieve the same objective. The experts re-examined some known footage of the suspect and noticed that he had an unusual and distinctive gait. The analyst took frames from the known footage that highlighted the suspect’s legs and feet, and did the same with the CCTV exhibit footage. In this way, the analyst provided comparative still images to show the similarities between the legs and feet of the known footage and in the CCTV footage. The analyst also edited several sequences to show side-by-side, to highlight the similarities of the unusual gait between the films, which enabled the suspect to be identified. The truth behind the digital forensic analysis and enhancement of CCTV footage may not be quite as quick and spectacular as police dramas may lead us to believe. But with the wide range of analysis and enhancement tools and techniques available, CCTV footage can still be a valuable source of information during a digital investigation. For more information on CCTV analysis or CCL’s other products and services please call us on 01789 261200, email edisclosure@cclgroupltd.com or visit www.cclgroupltd.com Nathan is an digital forensics specialist at CCL Group - the UK’s leading supplier of electronic disclosure and digital forensics consultancy, including: computer forensics, mobile phone forensics and cell E disclosure. .


Cctv Analysis in Digital Forensics