What documentary can the technique that was devised as a "gag" by Reznor be seen?
Visual elements employed during Nine Inch Nails concerts have often included numerous lighting, stage and projection effects employed to accompany and augment presentation.  Prior to the Fragility tour in 2000, Reznor reflected that "I’ve adopted a philosophy of the way to present Nine Inch Nails live that incorporates a theatrical element. I want it to be drama. I want my rock stars to be larger than life, you know? The Kurt Cobains of the world, I’m sick of that shit. I don’t want a gas station attendant being my hero. I grew up with Gene Simmons. I grew up with Ziggy Stardust."Many songs are typically accompanied with specially designed visual aids, including synchronized lighting effects and projected stock-footage montages.  Early performances of the song "Hurt", for example, were accompanied by a projected montage of clouds, charred bodies, mushroom clouds, maggots, and war refugees, a performance of which is featured in the song's music video.  Recent performances of the song, however, have featured less lighting effects.
Since 1999, the visual presentation of Nine Inch Nails live shows have been directed by Rob Sheridan, while Bill Viola designed a large triptych display for the Fragility tour.  The images displayed on the triptych focused on storm and water imagery.  And All That Could Have Been features an audio commentary track by Viola describing the display and his inspirations for it.For the Live: With Teeth tour, Roy Bennett and Martin Phillips were responsible for the lighting design and stage design respectively.  Bennett explained in a 2005 interview that much of the lighting was done using a series of LED lights arranged in "stalactites or stalagmites [formations] to tie in to the album artwork".  DLP projectors were also used to project images onto a gauze screen in front of the stage.
Using the gauze projection-screen, Phillips, Reznor, and Sheridan devised a "gag" where they projected "a sheet of glass shattering onto a downstage kabuki scrim that would drop as the glass shatters fell. ... We settled on Trent swinging his guitar at the gauze [and] shattering it, but with all the pieces falling up as the [screen] flew out".  This technique can be seen in the tour documentary Beside You in Time.  In contrast to the lighting of previous tours, Performance 2007 featured minimal lighting that was designed to shadow Reznor and the band.The visual elements of the live shows has been subject to much commentary.  The Boston Globe described the Fragility tour as "one of the most outstanding light shows in memory".  A reviewer from the Contra Costa Times described a Live: With Teeth performance as being "heightened by just the right amount of dark purple or blue spotlights, with up-lighting from the stage front, giving the band a horror-flick feel".
Beside You in Time