Is it possible to add an image to a html page that only shows up when sharing page on Facebook/G+? The image should not be visible in the html page since it contains a Flash game, but I would like it to show up when you post a link to the url on social sites.
yes you can. Just add
<meta property="og:image" content="http://www.domain.com/shareimage.jpg"/>
at the top of the html page that you want to share. The image path that you use here will come up in the facebook.
Refer Open Graph
Thanks. It works like a charm on Google Plus, but not on Facebook. The title appears, but not the description or the image.– MattiasDec 3, 2011 at 6:27
Just found this: developers.facebook.com/tools/debug– MattiasDec 3, 2011 at 6:28
For the description and title you need to add : "og:description" and "og:title" meta tags similar to "og:image". Please refer the link in my answer. Dec 3, 2011 at 6:45