When information is recorded onto magnetic media, be it analog or digital, the recording device leaves a signature within the recording. This is also true when information is erased, or when the recording device has been paused, stopped or started. When magnetic media is viewed, only the image can be seen, but with forensic equipment and analysis, more information can be collected from the recorded medium. This information may include whether the recording has been subjected to alteration or editing. It may also indicate whether the recording is a copy or an original.
Analysis of digital media (not on magnetic substrate) is not so simple. Various forms of digital media are increasingly being employed for capturing video; HDD, SSD, DVD, CD, Flash Drives, etc.. Digital recordings do not contain the same trace signs of tampering as magnetic media. It is still possible to determine whether a digital recording is altered or edited, but this process involves separating the layers of digital recording to look for anomalies from one layer to the next.