Best solution for a group gallery

I can solve this but would like feedback for the best solution for creating a group gallery.

Each user can create a gallery of their own and add images into the image collection each with a gallery_id. Do I keep a group collection where I link gallery_id with a group_id, where all users in the group have the same group_id, and then get the images for each gallery? Or do I add a field for each image with the group_id and get all images by that?