JFBConnect implements Open Graph tags which are hidden HTML tags that can be inserted onto the page to let Facebook and other social networks what content you want to share. By default, JFBConnect will set the title and description on the page to whatever the meta title and description are.
To set the image, we recommend using the Open Graph plugins included with JFBConnect for any extensions you have enabled, like Open Graph - Content (for Joomla Content), K2, EasyBlog and some others.
Additionally, on any page or your site (even in extensions we don't have Open Graph plugins for) you can use our Easy-Tags to set an image or custom title or description for the page, like:
{SCOpenGraph title=Great title for the page}
{SCOpenGraph description=Here's a description for the page}
{SCOpenGraph image=http://site.com/image.jpg}
I hope that helps get you started, but if you need anything else, please let us know.
Thanks,
Alex