Content-based tag processing for Internet social images

Online social media services such as Flickr and Zooomr allow users to share their images with the others for social interaction. An important feature of these services is that the users manually annotate their images with the freely-chosen tags, which can be used as indexing keywords for image search and other applications. However, since the tags are generally provided by grassroots Internet users, there is still a gap between these tags and the actual content of the images. This deficiency has significantly limited tag-based applications while, on the other hand, poses a new challenge to the multimedia research community. It calls for a series of research efforts for processing these unqualified tags, especially in making use of content analysis techniques to improve the descriptive power of the tags with respect to the image contents. This paper provides a comprehensive survey of the technical achievements in the research area of content-based tag processing for social images, covering the research aspects on tag ranking, tag refinement and tag-to-region assignment. We review the research advances for each topic and present a brief suggestion for future promising directions.