1. A method of determining an annotation for a particular image, the method comprising: determining a plurality of images related to the particular image, the plurality of images stored in one or more computer systems; identifying a plurality of annotations associated with the plurality of images; generating an ontology for the particular image wherein the ontology comprises: a plurality of terms, the plurality of annotations, and the plurality of images arranged in a hierarchy with the plurality of annotations being downstream from the plurality of terms associated with a highest level of the hierarchy, and the plurality of images being downstream from the plurality of annotations, and a plurality of links defining relationships between respective terms, annotations, or images, wherein each link is associated with a respective relevance value indicating a measure of relevance between two respective terms, annotations, or images connected by a respective link; determining a total relevance value for each term associated with the highest level, wherein for each term associated with the highest level, the total relevance value is a sum of relevance values of links downstream from the term; and associating one of the plurality of terms having a highest total relevance value with the particular image as an image annotation.