Cool - now that JS supports it, the per-photo focus is likely a significant improvement over just noting the gallery. And being able to set the image to the photo is almost necessary in such a situation.
What would be ideal is likely something you can't do though - the "share on facebook" checkbox when uploading. But that's JomSocial core code.
Now, that said, it's something I'll likely code-in as a template override in JomSocial. I can add the share option, default the checkbox based on the user's preference from your component, and then sniff that value when your open graph action is triggered.
This would let me then re-submit the action to Facebook as implicitly shared, something I'd really like to have
If I do this, I'll toss you the code in the override. It's likely something you don't want to support (or should!) but getting it out there simply as a documented example would be helpful to others who want to do it.
Getting your open graph action to be per-photo is first, though.