<Dd> One of the techniques used to hide data is via steganography, the process of hiding data inside of a picture or digital image . An example would be to hide pornographic images of children or other information that a given criminal does not want to have discovered . Computer forensics professionals can fight this by looking at the hash of the file and comparing it to the original image (if available .) While the image appears exactly the same, the hash changes as the data changes . </Dd> <P> When seizing evidence, if the machine is still active, any information stored solely in RAM that is not recovered before powering down may be lost . One application of "live analysis" is to recover RAM data (for example, using Microsoft's COFEE tool, windd, WindowsSCOPE) prior to removing an exhibit . CaptureGUARD Gateway bypasses Windows login for locked computers, allowing for the analysis and acquisition of physical memory on a locked computer . </P> <P> RAM can be analyzed for prior content after power loss, because the electrical charge stored in the memory cells takes time to dissipate, an effect exploited by the cold boot attack . The length of time that data is recoverable is increased by low temperatures and higher cell voltages . Holding unpowered RAM below − 60 ° C helps preserve residual data by an order of magnitude, improving the chances of successful recovery . However, it can be impractical to do this during a field examination . </P> <P> Some of the tools needed to extract volatile data, however, require that a computer be in a forensic lab, both to maintain a legitimate chain of evidence, and to facilitate work on the machine . If necessary, law enforcement applies techniques to move a live, running desktop computer . These include a mouse jiggler, which moves the mouse rapidly in small movements and prevents the computer from going to sleep accidentally . Usually, an uninterruptible power supply (UPS) provides power during transit . </P>

A simplified guide to forensic audio and video analysis. national forensic science technology center