Flickr is a popular photo sharing website where you can upload photos into albums that can be then organized, tagged and shared with others. Flickr allows you to make a group and add photos, videos, comments and much more to share with other group members. If you are a member of this group, then you can easily add photo to the group pool. And, if you are not a member then you need to join the group. Only group members can add photos to the group pool. To add a photo to a group, go to photo's page and click actions menu and click 'Add to a Group' link and then choose a group where you want to add a photo. Only you and the group administrator can remove a photo from a group pool.
You can install PicBackMan's Flickr uploader for Mac from the website and start backing up photos and videos.