In our Drupal 7 site, we are using Organic Groups to create private groups. Users are also able to upload content to a gallery (using custom Content Types "Gallery image" and "Gallery video"). On users' profile pages, we are showing a carousel of their N most-recent uploads, with a View using a Contextual Filter on Author
We would like to add a similar carousel to each OG group page, showing the most-recent N uploads by members of the group. [Edit: This is uploads to the general Gallery, the OG groups do not have their own galleries.] If it makes a difference, almost all users will be members of more than one group (for reasons that are unimportant, there are two kinds of group: geographic groups and interest-based groups).
This seems like it's probably very easy, but I just can't see how to do this, either from the View's Contextual Filters or the View's Relationships.
Am I missing something obvious?