A caption is descriptive text that appears below an image. InDesign provides several methods for creating captions that display the image metadata you specify. InDesign provides a special caption variable that displays the specified metadata of an image. If a text frame containing the variable is next to or grouped with the image, the variable displays the metadata of that image. You can generate a caption from an existing image or while placing it, and you can create a text frame that contains a caption variable.
For video tutorials on generating captions from metadata, see http://tv.adobe.com/go/4958/.