Friday, February 25, 2011

Crime Scene Investigation: Using the right metadata to catch criminals

From the British Journal of Photography: "Police forces risk letting the guilty go free if they don't address their procedures for using digital images as evidence in court. Mark Wood explains why a raw workflow is good for us all.

For some, debates about the veracity of photographic images rage, others have simply moved on from hackneyed arguments about truth and testimony. However, in police work and forensics, questions about digital photography have not been fully addressed. In the UK, there is no common practice on the capture and storage of digital photographs. The guidelines, such as they are, are open to interpretation by each of the UKʼs police forces, and a key issue centres on whether to shoot raw or JPEG.

It is essential that evidence is permissible in court, so the challenge is to foresee problems with a form of evidence such as digital image data. In time, a form of evidence may be found to be unreliable, and therefore discredited. Science drove the use of DNA profiling and, though science is a broad term, similar rigour has to be applied to the use of digital imaging in police work. There is still the notion that anyone who picks up a DSLR is a photography expert, or that being able to tick a box on a staff development form is a panacea for the complexities of image processing.

The leviathan of the legal system moves at a different pace from the fast-changing landscape of digital imaging; official guidelines can be out of step with operational needs. So the diverse and ambiguous implementation of the ACPO (Association Of Chief Police Officers) digital imaging handling guidelines in 2002 could well lead to convictions being quashed on the technicalities of photographic veracity. Though having some flexibility when interpreting the guidelines can make workflows fit for purpose, each force still has its own Standard Operating Procedures and, as long as those protocols are followed, then all is deemed to be in order. There is a disturbing reliance on JPEG files in several forces, for example, and no matter how secure a system might be, it is extremely difficult to prove that JPEG evidence has not been tampered with. In court, an imaging officer might have to testify that a photograph is a true representation of the captured data and has not been manipulated, yet the court must take their word for it. Immutable evidence is required.

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