Thank you for the image. That helps explain things. I see the post is coming from an Open Graph Action after a user uploads an image in JomSocial. Can you check the following:
* When you click that post, what link are you brought to on your site?
* If you are not logged into your site, does the link still work, or are you brought to the JomSocial login page? If so, this is what would happen to Facebook too.
* On whatever page you are brought to when you are not logged into the site, try running it through the
Facebook URL Debug Tool
. That will show you what Facebook 'sees' on the page and should help determine why the preview looks like that.
I hope that helps get you started, but if there's anything else we can help with, just let me know.
Thanks,
Alex