Thanks for your review. But your problem have nothing to do with my module. Facebook renders your page and takes the first image. If you want facebook should use an article image, you should use Open Graph tags.
This is a plugin which do it for you: http://extensions.joomla.org/extensions/site-management/seo-a-metadata/open-graph/20596
TL:DR - This is a great extension but be very careful to check and resolve your W3C validation errors.