UnityAr provides an interface to the ARToolkit. Local connected webcams are used as input source for the pattern recognition. This interface allows to detect multiple ARToolkit marker from the videostream and provides the position and rotation of each marker in the 3D scene.
A free beta version is available on our website: http://produktion.weltenbauer.com on the "entwicklungen." section.ARToolKit is a computer vision tracking library that allows for the creation of augmented reality applications that overlay virtual imagery on the real world. To do this, it uses video tracking capabilities in order to calculate the real camera position and orientation relative to square physical markers in real time. Once the real camera position is known a virtual camera can be positioned at the same point and 3D computer graphics models drawn exactly overlaid on the real marker. So ARToolKit solves two of the key problems in Augmented Reality; viewpoint tracking and virtual object interaction. (From Wikipedia)
ARToolkit Details: http://www.hitl.washington.edu/artoolkit
CodeVis VidCap Details (Video stream input): http://www.codevis.com/vidcapture