Display Image Descriptions or Captions?

I would like to display image descriptions or captions when opening the main, large image using Auto Thickbox. The Auto Thickbox has the option to show the description when opening the full sized image, but even when I fill in the description of the image, it does not show. The Alt/Title does show however when I use that option. So how would I go about this?

http://www.dwdallam.com

http://wordpress.org/extend/plugins/nextgen-gallery/