thanks for any idea and answer.
A quick google search turned up nothing for me on a C#/mono interface to webcam hardware. Assuming that no such API exists, I would recommend creating a native code plugin interfacing with a C/C++ api for grabbing webcam frames. OpenCV is one example of such an api.
Here is a windows plugin for Unity that let you access local connected webcams:
Well a few hints, Unity is OPENGL not DirectX, thus you need to know which version of OpenGL that Unity is using, now, if Unity 2.5 is using OpenGL 2.0 or 3.0, then good, otherwise, forget it.
http://www.opengl.org/registry/specs/NV/video_capture.txt
Now, since you have to own PRO to make this work, this is where you begin, doing this work is an advanced programming feature, so I wouldn’t recommend attempting this unless you have figured out how to utilize OpenGL → Unity pipeline directly. If you have figured that out, then this will be a breaze. The good thing about this, is that you can do video streaming and not have to drop the files as images to a folder and then read the images. Stream the image from the capture device to Unity. Although the only thing is, I am not sure if you can use the Unity version of render to texture to get this to work.