A user annotates a shared document with text, sound, images, video, an e-mail message, graphics, screen snapshots, web site snapshots to share with others. The document and its annotations are stored in a digital object repository to which other users have access. Within the closed collaboration system, only users who are authenticated may upload digital objects, annotate digital objects and view objects and their annotations. The user sends a message to other users to invite them to view the object and its annotations and to add their own annotations. An annotated object generates an alert for all of the invited users. A remote authentication gateway authenticates users and has a repository for user metadata. Digital object repositories are separate from the authentication gateway, thus providing for disintermediation of the user metadata from the digital object data. The collaboration system may be hosted by a third party on a server computer available over the Internet that displays a web site. A user is not required to have collaboration system software on his or her computer and may annotate any image on the web site for later viewing by other users of the web site.