1. A computer-implemented method performed by a data processing apparatus, the method comprising: providing, by a computer, an image to an image processing apparatus, the image being defined within a first bounded region; receiving, by the computer, from the image processing apparatus a plurality of object search results for the provided image, each object search result identifying: a respective pre-specified object class to which a respective object belongs, the respective pre-specified object class being one of a plurality of pre-specified object classes; and a respective second bounded region in which the respective object is located, the respective second bounded region being within the first bounded region; wherein at least one of the respective pre-specified object classes specified by the object search results is different from each other respective pre-specified object class specified by the object search results; determining, by the computer, for each object search result, a respective rank score from characteristics of the respective second bounded region identified by the object search result, comprising: determining a first centroid of the first bounded region; determining a respective second centroid of the respective second bounded region; determining a distance between the first centroid and the respective second centroid; and determining the respective rank score based on the respective distance; ranking, by the computer, the object search results according to their respective rank scores; and providing, for each ranked object search result, a result image to a user device for display according to the ranking, the result image including a portion of the provided image defined by the respective second bounded region identified by the ranked object search result.