Michael,
Can you let me know a JomSocial URL of a page that doesn't share properly for you?
I was just testing with my own account at the following URL, which has the following Open Graph URL Debug report:
developers.facebook.com/tools/debug/og/o...lbum%3Falbumid%3D161
The issue there is that JFBConnect is actually doing things right by selecting the main photo of the album to be shared. However, the image itself is too small, which makes Facebook look for another image to use instead. For some reason, it seems to always be choosing the following image:
pentax-akademie.de/images/pentax-akademie-logo-weiss-2.png
That's your logo, which makes sense, but since it's pretty much white on a transparent background, it looks blank in the share area.
What I'd recommend is going to the JFBConnect -> Open Graph -> Configuration area and setting a better default image for Facebook to fall back to. That can be a different logo or whatever else you want. In the configuration area's "Default" box, simply add:
image=http://site.com/link-to-a-good-default.jpg
I hope that helps at least explain what's going on, but if you need more info, just let me know.
Thanks,
Alex