A system, comprising: a data processing apparatus; and software stored in non-transitory computer readable storage medium storing instructions executable by the data processing apparatus and that upon such execution cause the data processing apparatus to perform operations comprising: for each resource in a plurality of resources, wherein each resource includes one or more images and text that is separate from each of the one or more images; determining, by a data processing apparatus, and from the text of the resource, resource topics described by the text of the resource; for each of the one or more images, processing, by the data processing apparatus the image to determine a set of image topics that describe topics to which content depicted in the image belongs, determining, by the data process apparatus, one or more topic match scores, wherein each topic match score is a measure of relevance of one or more of the image topics of the image to one or more of the resource topics of the resource; storing in an index, by the data processing apparatus and for the image, data that describes the image topics for the image, resource topics for the resource, and the one or more topic match scores for the image; in response to an image seeking query, accessing previously determined resource topics, image topics, and topic match scores for particular candidate images by accessing information stored in the index. a data processing apparatus; and software stored in non-transitory computer readable storage medium storing instructions executable by the data processing apparatus and that upon such execution cause the data processing apparatus to perform operations comprising: for each resource in a plurality of resources, wherein each resource includes one or more images and text that is separate from each of the one or more images; determining, by a data processing apparatus, and from the text of the resource, resource topics described by the text of the resource; for each of the one or more images, processing, by the data processing apparatus the image to determine a set of image topics that describe topics to which content depicted in the image belongs, determining, by the data process apparatus, one or more topic match scores, wherein each topic match score is a measure of relevance of one or more of the image topics of the image to one or more of the resource topics of the resource; storing in an index, by the data processing apparatus and for the image, data that describes the image topics for the image, resource topics for the resource, and the one or more topic match scores for the image; for each resource in a plurality of resources, wherein each resource includes one or more images and text that is separate from each of the one or more images; determining, by a data processing apparatus, and from the text of the resource, resource topics described by the text of the resource; for each of the one or more images, processing, by the data processing apparatus the image to determine a set of image topics that describe topics to which content depicted in the image belongs, determining, by the data process apparatus, one or more topic match scores, wherein each topic match score is a measure of relevance of one or more of the image topics of the image to one or more of the resource topics of the resource; processing, by the data processing apparatus the image to determine a set of image topics that describe topics to which content depicted in the image belongs, determining, by the data process apparatus, one or more topic match scores, wherein each topic match score is a measure of relevance of one or more of the image topics of the image to one or more of the resource topics of the resource; storing in an index, by the data processing apparatus and for the image, data that describes the image topics for the image, resource topics for the resource, and the one or more topic match scores for the image; in response to an image seeking query, accessing previously determined resource topics, image topics, and topic match scores for particular candidate images by accessing information stored in the index.