As image collections become ever larger, effective access to their content requires a meaningful categorization of the images. Such a categorization can rely on clustering methods working on image features, but should greatly benefit from any form of supervision the user can provide, related to the visual content. Semi-supervised clustering learning from both labelled and unlabelled data-has consequently become a topic of significant interest. In this paper we present a new semi-supervised clustering algorithm, Pairwise-Constrained Competitive Agglomeration, which is based on a fuzzy cost function that takes pairwise constraints into account.