Your group gets a basic group image gallery. Click on 'gallery' from the navigation menu and click 'Add a new image to the group gallery'.

You may upload images to the site from your hard drive by clicking the 'browse' button in the 'Image' field. Fill out a title and optionally a brief description.

You can choose any extra groups to add the image to and/or whether or not you want to have the image be only visible to group members by clicking 'Groups'. You may edit or delete the image by clicking the 'Edit' tab when viewing the image (go to the image gallery it's in, click on it, click 'Edit').

There is currently no sub-galleries for group images and don't bother asking for that. The fact that groups even have their own gallery is a luxury.