1. A computer-implemented method, comprising: under control of one or more computer systems configured with executable instructions, receiving a search request specifying query content, the query content characterized by query descriptors at each of a plurality of scales; for each content piece of at least one portion of a content collection: identifying a subset of content descriptors of the content piece at each of the plurality of scales, the content descriptors characterizing and describing one or more regions of the content piece, each of the subset of the content descriptors at a respective scale of the plurality of scales corresponding to at least one portion of the query descriptors at the respective scale; determining a size of the query content to generate respective first proportion thresholds with respect to the size of the query content; determining whether a respective first proportion of the subset of the content descriptors at each respective scale is greater than the generated respective first proportion threshold corresponding to the respective scale, the respective first proportion threshold comprising a region size threshold corresponding to the respective scale; and selecting the content piece for inclusion in a matching content subset of the content collection when at least one of the one or more regions of the subset of content descriptors includes a proportionate size greater than the respective first proportion threshold; and providing the matching content subset in response to the search request.