This effect is now available fully assembled for sale in single units or sets of three with options for surface or flush mounting. I also have the frames with computer-cut 2-way plexiglass mirror available to assist your DIY efforts. Please contact me through instructables or drop me a line at firstname.lastname@example.org for more information.
I created a "spooky face in-the-mirror" special effect in 2009. The effect is of three green glowing framed mirrors that have a spooky face which appears to move from frame to frame on a continuous loop throughout the event. The effect was created with 3 UNG DRILL frames from IKEA, which I painted fluorescent green. The UNG DRILL frames come with clear plastic which you can either use as a measuring guide to have 2-way mirror custom routed/cut, which I did, or you may try to use a 2-way mirror film to apply to the included plastic. I purchased 3 of the most inexpensive widescreen 19" LCD's I could find. The initial installation enabled me to place widescreen LCD panels behind faux walls, mounting the frames flush on the walls. I wanted to be able to use the frames elsewhere when I would have to have the LCD display taking up space behind the frame, so I designed an ornate black frame inspired by wrought iron filagree which was cut from black Sintra, a pvc sheet product which can be computer cut by a CNC router. I used a heat bender to raise the framework out from the wall just enough to accomodate the LCD panel. It works very well at hiding the display and visually anchors the mirror to the wall.
To make the video I recorded my friend Ryan's face with a black t-shirt pulled over his head to expose just the very front of his face. I wanted it to look like a floating face, not a whole head. I lit his face from below to enhance the ghoulish quality of the image. This was all done in front of a black backdrop. His face had white makeup on it, but I'm not certain that was entirely necessary. Because the LCD displays are mounted on their side, the camera was also on it's side to record the footage.
The video was then edited in Final Cut Pro to enhance the contrast of the face and the black background. Then, an important step was to alter the color to look as though the face was lit with ultraviolet (black) light and was U.V. reactive. U.V. reactive white looks blueish under UV light, so I gave the image a tint that matched that same hue of blue. Because the LCD display gives off an illuminated image, and the altered face footage appears to be reacting to black light, the whole display appears to be glowing exclusively from ultraviolet light. This makes the effect a bit more mysterious and avoids simply looking like a "tv behind a mirror". Both the fluorescent frame and the face glow at the same level of brightness. In person, the effect is brighter than it appears in the attached video, but rather the way it does in the photos.
To create the effect that the face moves from frame to frame and never is in two places at the same time, I created three separate video tracks, one for each frame. Then created DVD's in DVD Studio Pro that automatically start playing when the dvd player powers on. Then I used three dvd players of the same manufacturer and model, one running to each mirror/video display. By using a remote control I am able to turn on all three dvd players at the same time so they are synced. The dvd's are programmed to automatically loop. They seem to stay in sync at least for 8+ hours.
UPDATE: For a simpler option with no moving parts, I recommend the Micca Speck Ultra Portable Digital Media Player