Help with a distance sensor...

I am an art student in London, and am looking for help with a project using a distance sensor...
I intend to show a small screen with images on, and want the images on
the screen to change depending on the distance of the viewer to the screen.
The images will be of eyes looking at the screen, but the nearer the viewer is to the screen, the more the eyes will look away. By using a small screen, the viewer will be forced to get close to it in order to see what it is showing.
Any help would be greatly appreciated on i) types of motion/distance sensors, and ii) how I may be able to connect them to computer/DVD player so that the images shown will change depending on viewers' distance.
Any other ideas would be useful too - thank you! Tom
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Do you want to learn robotics? Or do you just want someone to tell you how to do it?
If you have some programming backround and want to learn robotics then you can start with sonic range sensors such as those from Devantech or even stereo vision recognition (which is becoming more simple). This would probably cost you less than $300 US.
If you have absolutely no clue of programming and robotics, but simply want somebody to tell you how to do it - my bid is $1000 US (for software creation and verification). A complete unit would bounce that up to a minmum of an additional $500 US for hardware.
Certainly you could achieve your goals for less, but if your educational focus does not include electronics and programming (as my education doesn't save me a bundle on lawyer fees or medical expenses), I don't consider this an unreasonable charge.
Bart
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