General case, we can use these scripts below to display camera on the scene in the Unity3d.
WebCamTexture wc = new WebCamTexture ();
GameObject.Find (“/plane”).renderer.material.mainTexture = wc;
But sometimes we want to save camera to image, or realized video streaming. We can use WebcamTexture.GetPixels() and Texture2D.SetPixels(), but you must noticed returning width and height.