How is the og:image URL being inserted? Since we don't natively integrate with Ohanah, I'm assuming you're using the {JFBCGraph image=xxx} tag. If that's the case, make sure that the full URL is used in the image=xxx part, including the scheme and domain (
site.com/link-to-image.jpg). JFBConnect doesn't insert this automatically if you use relative links.
As for setting the type, URL, image, description, or any other Open Graph tags, if you can detect that JFBConnect is installed, you can simply add the {JFBCGraph type=...} tags into the page, and JFBConnect will translate them to the proper og:xxx tags. Use the {JFBCGraph} syntax will override the defaults that we set, but if the tag isn't set, we'll try to set the page up with Open Graph tags automatically.
If you can detect that JFBConnect isn't installed, then obviously, you can add the og:xxx tags to the document head using JDocument. It'd be best if you could do the auto-detection to prevent duplication of tags though. Something as simple as checking if either the jfbcsystem plugin is enabled or even if the /components/com_jfbconnect directory exists would work.
Hope that helps, and by all means, feel free to ask for any help on integration. We love working with 3rd parties to make sure we're compatible. It saves us from headaches later, and also helps for promotion going both ways
Thanks,
Alex