Anyone catch this past Monday's CSI Miami? They butchered technology again.

Grain of truth: on video tape, sometimes if the erase head wasn't working right you might be able to see a visible ghost of the previous recording.

Improper application: the team was analyzing a tape from a modern consumer camcorder and they somehow saw a ghost of the previous recording in the background. After fiddling with some knobs, they were able to produce a near-perfect version of the previous recording, complete with audio.

Technical impossibility: this was a modern camcorder, it at least looked like MiniDV. Digital camcorders can't leave visible "ghost images" of previous recordings, even if the erase head is bad. It's recording and later decoding 1s and 0s, nothing like an analog recording - you either get perfect reproduction, or it's a garbled mess. The most likely symptom of a bad erase head is dropouts and other corruption on playback. When they started to work on this, I was initially considering giving them a SLIGHT pass... I mean perhaps this couple really was using some ancient 8mm camcorder. But then the tech had to go a talking about how he was "recovering digital data"... destroying that possible out.

Even if...: Let's say that the erase head was bad. Let's say that there really was a "digital ghost" in the background. And let's say that they pulled off the impossible and were somehow able to isolate most of the original recording's faint 1's and 0's from the much stronger 1's and 0's made by the new recording. Optimistic, let's say they somehow managed to get back at least half of that original data. There is still no way they would get near-perfect video and audio reproduction from that. On digital recordings, when a little bit of data is garbled, it affects a much larger area (as soon as the error correction is even slightly overwhelmed). When a larger amount of the data is garbled, you'd get a horrible mess. Moving items in the wrong place. Flashes of color and other corruption as bad keyframes come up. Basically it would barely be recognizable as video, never mind what they presented which was 98% perfect with just slight pixellation. They also had absolutely perfect sound - in reality it would be nothing but a mess of loud snaps, pops, crackles and static.