A device for segmenting an image comprises a user input (301, 305, 307) for receiving segment indications and boundary indications for the image. Each segment indication identifies a set of pixel regions and a relationship between the set of pixel regions and an associated segment class of a plurality of segment classes. Each boundary indication identifies a boundary between pixels belonging to different segment classes. A segmentation processor (309) then segments the image into the plurality of segment classes in response to both the number of segment indications and the number of boundary indications. Specifically, a propagation of values linking the pixel regions to segment classes are propagated based on the segment indications with the propagation being constrained (e.g. attenuated or blocked) by the boundary indications. The invention may improve or facilitate interactive image segmentation e.g. for frames of a video signal.