You can display absolutely any HTML in this caption.
Adjust the width/height and the location (top/bottom/left/right) as you wish.
To adjust the background, fonts and borders, open the magiczoomplus.css file.
All these options are described in the integration guide.
You can even add forms, images and links in here.
Title at top, caption to right
Inner zoom, title at top
Title at top, caption to left
Inner zoom, title at bottom