It depends on your target audience and the expectations your design gives user; some ideas will work in some situations, others will work in others, but there i

It depends on your target audience and the expectations your design gives user; some ideas will work in some situations, others will work in others, but there is no general solution. Some ideas: 1. Content belongs to the group; once a user is out of the group, they can't get to it, even if they contributed it themselves. Possibly good if your app will have a corporate focus (former employees losing access to confidential company materials even if they created them is the norm). 2. Users own content, but grant irrevocable rights to access and modify the content to the group. The rights persist even after the user has been removed. 3. Creating users own content, and can always get to it, even after they are removed. Users can grant groups rights to access content. This permission can be revoked even after the user has left the group, at which point the group can no longer access the content. Revocation of rights is a separate action to deletion from the group. 4. Content is associated with the creator, and when the creator is deleted from the group, their content is assumed to be uninteresting and so is no longer part of the group. Perhaps good if you have big groups, and expect spammers to try to join; deleting users from groups is an anti-spam measure. Note that users could save content outside of your site if they wanted to; if you really needed to, you could fingerprint all images and detect if they were later re-uploaded with a different purported creator. Whatever you do, you should make sure to make users agree to grant you a license to do what you want to do - UGC may be copyrighted by the user, and if you don't let them retract content from groups they are no longer in, for example, you had better have ensured they agreed to grant you an irrevocable license. Getting an experienced lawyer to check the language would be a good idea.