The Mediaeval 2013 Retrieving Diverse Social Image Task addresses the challenge of improving both relevance and diversity of photos in a retrieval task on Flickr. We propose a clustering based technique that exploits both textual and visual information. We introduce a k-Nearest Neighbor (k-NN) inspired re-ranking algorithm that is applied before clustering to clean the dataset. After the clustering step, we exploit social cues to rank clusters by social relevance. From those ranked clusters images are retrieved according to their distance to cluster centroids.