Video Mapping

I'm exploring all different avenues, searching for a suitable/effective way for the visual aspect of my project to be displayed.
My first idea, which has been the only idea I had generally thought of once changing my idea from an art project to a media installation, was to use cameras as sensors.
I could make web cameras that are attached to a projector and secured to walls within the room track peoples movements, working almost like the motion sensors on the Nintendo Wii or Xbox Kinect (obviously not as sophisticated though).
Once people come within a certain distance of the cameras this could then trigger the projector to play. However this doesn't involve any user interaction and my idea really consists of there being a heavy influence of user participation between them and the tree.
If it is some how possible I could maybe have the web cameras focus on the organs that I want the users to interact with, and once they become in a close enough proximity with the organs the cameras could pick this up and activate the projector. Almost giving the illusion to the user that somewhere within the organ is some kind of sensor that works together with the projector.
I think this could be a tricky and clumsy process as it may become too awkward for the cameras to only act upon the users coming into a certain distance with the organs.
There is quite possibly a more functional and smaller scale piece of technology out there that is more suited to adapt to the functionality I am trying to incorporate into my piece of work. I obviously just have to keep searching.
I nice idea that I came across through the course of my research that could send my installation into a whole other direction was video mapping.
Video mapping if you are unfamiliar with it is a projection technology sometimes referred to as projection mapping that is used to change two or three-dimensional shapes into a form of canvas where visuals can be displayed.    
Through the use of specialised software objects are mapped out in a virtual environment. With the information gathered the software can then work together with the projector to fit a desired visual or design on to the surface of the object.
If I was able to obtain this software for a reasonable cost and implement it into my work I could envision my project taking a drastic change of direction to what I had previously imagined.
Rather than just having the memories of a persons' life being simply displayed on a wall I could have them mapped onto the surface of the tree itself, and then maybe try to form some kind of interactivity based around this.The visuals could be constant or activated by the organs to project onto the tree.
It is definitely an idea to give some consideration to. However with every idea there are risks and factors that need to be worked out before even pursuing further development.
I will look into costs, attainability, functionality and dependency before I give this idea any more thought because I'm really set on the original way I imagined my installation to be.
Here is a short documentary I watched  to gain a little more insight into the methods behind the technology used to create a video map. Directed by Dane Luttik this short video reveals the ideas and functions behind  projection mapping, specifically for the use of VJs (Video Jockeys) as they are commonly known for using this form of technology.