12. One or more computer-readable storage media storing instructions that, when executed by one or more computing devices, cause the one or more computing devices to perform operations comprising: obtaining low-level features from each image in a set of images, wherein each image is associated with one or more labels in a set of labels; generating a high-dimensional representation for each image based on the low-level features of the respective image; generating a lower-dimensional representation for each image based on the high-dimensional representation of the respective image; generating a classifier for each label in the set of labels based on the high-dimensional representations of the respective images that are associated with the label or the lower-dimensional representations of the respective images that are associated with the label; and generating a respective combined representation for each image, wherein the respective combined representation of an image includes the respective classifiers of the one or more labels that are associated with the respective image and includes the lower-dimensional representation of the respective image, and wherein the respective combined representation for an image is generated according to 
 {tilde over (x)} ij =λ·w i +(1−λ)· x ij , where x ij denotes the lower-dimensional representation of the image, where {tilde over (x)} ij denotes the respective combined representation of the image, where w i denotes the respective classifiers of the labels that are associated with the image and where λ is a regularization parameter.
12. One or more computer-readable storage media storing instructions that, when executed by one or more computing devices, cause the one or more computing devices to perform operations comprising: obtaining low-level features from each image in a set of images, wherein each image is associated with one or more labels in a set of labels; generating a high-dimensional representation for each image based on the low-level features of the respective image; generating a lower-dimensional representation for each image based on the high-dimensional representation of the respective image; generating a classifier for each label in the set of labels based on the high-dimensional representations of the respective images that are associated with the label or the lower-dimensional representations of the respective images that are associated with the label; and generating a respective combined representation for each image, wherein the respective combined representation of an image includes the respective classifiers of the one or more labels that are associated with the respective image and includes the lower-dimensional representation of the respective image, and wherein the respective combined representation for an image is generated according to 
 {tilde over (x)} ij =λ·w i +(1−λ)· x ij , where x ij denotes the lower-dimensional representation of the image, where {tilde over (x)} ij denotes the respective combined representation of the image, where w i denotes the respective classifiers of the labels that are associated with the image and where λ is a regularization parameter. 13. The method of claim 12 , wherein the high-dimensional representations include a Fisher vector or a bag of visual features.