Activetuts+ (formerly known as Flashtuts+) has a simple tutorial on…how to detect intruders using Flash and a web cam. OK, you may not really need to use your digital signage to detect intruders but detecting motion can be an interesting way to add some interactivity or create interest in your digital sign.
Augmented reality is really hot these days and is only picking up steam. Some creative Flash programming and a $30 web-cam could be the poor man’s AR.