A novel automatic image annotation approach is proposed to bridge the semantic gap of content-based image retrieval.Our approach first performs segmentation of images into regions

followed by the clustering of regions to blobs using a semi-supervised image clustering algorithm with soft constraints which utilizing the visual and semantic information of images.And a graph-based algorithm is used to compute the probabilistic relation between concepts and region blobs which can be used to annotate new images.Experiments conducted on standard dataset demonstrate the effectiveness and efficiency of the proposed approach for image annotation.