Inverting aerial masking

[ChetHugo]

I have a aerial image that contains gray areas that I would like to mask.

I created a polygon for a mask but it masks the area that I need and not the two areas that I do not want.  How do I invert the area to be masked?  If there were not two areas to remove I would simply use a polygon around the gray area.

[m_neer]

Please forgive me if I'm off here - but I believe if its just a single image you can merely import the image into a image mosaic dataset and merely adjust the footprint boundary.   Thus limiting the image to the footprint boundary.