I'm using this solution to create image galleries in a SP 2013 Online site: http://www.getinthesky.com/2014/04/sharepoint-image-gallery-doesnt-suck/
The script uses the image alt/title tag to display captions for an image. I modified this line to pull in the "caption", but it displays as "undefined" which usually means the field is not in the view:
jQuery("#galleria").append("<img src='" + jQuery(this).attr("href") + "' alt='" + jQuery(this).attr("alt") + "' /> ");
In theory the picture library's description field is supposed to populate the alt tag but I'm not sure if it does. Anyone have any light they could shed on this?