Evaluating recorded evidence principally involves an examination to determine if tampering has occurred, whether intentional or accidental. In evaluating video-recorded evidence, the intention is to determine if anomalies or editing has taken place. These anomalies or edits are usually identified by irregularities in images, frame rates, time comparisons, acoustic signatures and other factors.
There are some basic anomalies, which usually denote tampering in recorded evidence. These include:
- Image jumps or anomalies in movement or location of items in the picture. Visual non-sequiturs.
- Dropouts – Signal loss where nothing, not even ambient noise, is recorded.
- Frequency changes – During various conversations, a speaker’s frequency typically changes.
- Spikes – Sounds that are short in duration but usually come from a recorder being stopped, started or paused.
For conclusions to be definitive on tampering, ideally but not necessarily, both the original recording equipment and original recording should be examined. Having access to original recordings and devices allows a determination as to whether these types of anomalies are intentional edits, or if they come from malfunctions in the media or recording equipment.
With the advent of digital recording and editing, evaluating recorded evidence has become much more complex. Digital recordings can be manipulated more easily than traditional analog recordings, making them much harder to evaluate for alterations. This increases the chances of altered tapes being verified as authentic, or that alterations escape notice even by experienced examiners. Digital recording and editing can make it incredibly difficult to determine if recordings have been altered, because once they are digitized, anomalies can disappear or be mistaken for typical digital recording markers. With digital recording becoming the norm, splicing tapes with razor blades to alter and edit their content has become obsolete. Special equipment for editing has also become outdated as software conveniently turns any computer into an editing studio.