I had trouble with imagePlane in maya 2015. As far as I know it is changed around maya 2013. ImagePlane now has a transform node so it looks like a standard object. You can create it from the menu: Create / Free Image Plane.
The strange thing is that when it is attached to a camera. It looks like a hierarchy (see below)
but it can't be unparent or reparent. So there is a special connection. In nodeEditor it also looks like a typical hierarchy where the transform node does not have any connection.
Only thing which can refer to some special condition is found in the scriptEditor when the imagePlane is selected:
select -r CameraShape->imagePlane1 ;
I experienced this syntax with
positionMarkers. Actually
I wrote about it before.
That is how I find out there is a term of
underworld nodes in maya. You can read about it
here or a more
here. Consider underworld node as a component like a NURBS CV and it will explain why it can't be unparented for eg.
So...we can create an imagePlane with MEL command (since maya 2013) like this:
imagePlane -name "myImagePlane" -camera "CameraShape";
And we can redirect" an existing imagePlane to another camera with the edit flag:
imagePlane -edit -camera "NewCameraShape" "myImagePlane";
I found the easiest way to get the imagePlane from the camera is to call this:
listRelatives -allDescendents "cameraShape"