Hello,
Sorry for the late reply. There is an example program that we provide on our public website that does exactly what you are looking for. It can be found at:
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3EE2156A4E034080020E74861&p_node=DZ52128&p_source=External
The title is call, "Saving the Image of a Measurement Studio Control into a File", and it does use the ControlImage() function to capture the image of a CWGraph as a .emf file. Take care and have a great day!
Regards,
Aaron B.
National Instruments