Thanks to the magic of the Internet, I figured out how to add a tab with a "camera widget" and an image overlay.  I would like to improve it a little...  There are three buttons and I would like the button click to change the image used for the camera overlay. 

Something like: btnOverlay3.onClick -> videoDisplay.image = "someimage.png"

Obviously I have no idea what the code needs to look like or where it goes.  I'm guessing that there would need to be a function in some script and then the name of that function goes into the button event.  I posted this to the "video probing" category because that is the goal, but maybe there is a better choice?

Thanks in advance for your help.
 

How did you get the crosshair overlay on top of the video? I tried using a png in the image part of the camera settings, but could not get it centered. The size of the camera window you specify does not seem to sync up with the size of the image in any way that I could understand.