7. The method of claim 5 , the social network kernel comprising a network of nodes and edges, each node corresponding to an individual represented in at least one content item of the plurality and each edge indicating a relationship between two individuals represented together in at least one content item of the plurality of content items.
5. The method of claim 1 , further comprising: training, by at least one computing device, the content kernel using at least the content feature information associated with each content item of the plurality of content items in the training set; training, by at least one computing device, the semantic kernel using at least the semantic feature information associated with each content item of the plurality of content items in the training set; and training, by at least one computing device, the social kernel using at least the social network feature information associated with each content item of the plurality of content items in the training set.