1. A computer-implemented method comprising: determining that one or more image features that are stored in a dynamic index that stores image features in an uncompressed form, are to be migrated to a static index that stores image features in a compressed form, the static index including one or more existing sets of image features, wherein both the dynamic index and the static index are used by an image search system to identify images that match query images; in response to determining that the one or more image features stored in the dynamic index are to be migrated to the static index, classifying the determined one or more image features that are stored in the dynamic index in the uncompressed form and that are to be migrated from the dynamic index to the static index into a particular, existing set of image features, according to a classification scheme associated with the static index; compressing the determined one or more image features that were classified into the particular, existing set of image features; generating a replacement set of image features including (i) the compressed one or more image features that were classified into the particular, existing set of image features, and (ii) one or more compressed image features from the particular, existing set of image features; and replacing the particular, existing set of image features included in the static index with the replacement set of image features.