Thursday, 9 June 2016

Interpretation of image and video evidence

The UK's Forensic Science Regulator has published a short useful document on Forensic image comparison and interpretation evidence. Much of what is says should be no surprise to law enforcement and forensic experts who understand video - but its still a useful document as it sets out some points and useful reminders.

Some Highlights:

If the subject to be identified is a substantial distance from the camera or only occupies a small proportion of the image, then the number of pixels that make up the subject may be low. As a result, the level of detail will be very limited and may not be suitable for reliable interpretation. Enlarging an image beyond its resolution will not add additional detail, but will only duplicate existing pixels resulting in a blocky or blurry appearance, depending upon the method of enlargement. The potential for enhancement of low resolution imagery is generally very limited.

There is a great example of how recorder compression artifacts plus 'enhancement' can lead to bad recovery. Based on the enhanced license plate below you may be quite sure the number plate reads DUN 150J, but the real plate is OUM T5GJ.

 Image enhancement should be approached with caution. If you want to know more about what enhancement or clarification can do, check out Kinesense CEO's post on "Video Clarfication: Fact or Fiction".