In the Web2.0 era, user generated content has<br>become the main source of information of many popular<br>websites such as Flickr. In Flickr, each user can share<br>his/her photos and browse others’ easily. Tagging system is<br>an important approach to the photo management in Flickr.<br>Users can browse photos by clicking their attached tags.<br>However, many photos have very few or even no tags,<br>because only the uploader can mark tags for the photo.<br>Meanwhile, when a user
