1. A method for enabling searching of focus items in images, the method comprising: using one or more processors to perform steps comprising: enabling search operations to be performed to determine images in a collection that depict objects having portions that are visually similar and not identical to a focus item that is included as part of an item of an input image, wherein the enabling search operations includes: programmatically analyzing each of the plurality of images in order to determine a signature of an item shown in each of the plurality of images; storing data corresponding to the signature of each item shown in the plurality of images; providing an interface in which a user is able to specify the focus item that is included as part of the item of the input image; determining a signature of at least a portion of the item of the input image that includes the focus item; determining search criteria that is based at least on the signature of at least the portion of the item of the input image that includes the focus item; in response to determining the search criteria, performing a search operation to identify a result that comprises one or more items that have a signature that satisfies at least some of the one or more search criteria so that one or more of the identified items includes portions that are visually similar and not identical to the focus item included in the search criteria; wherein performing the search operation includes performing an initial search operation on the collection using a shortened or truncated version of the signature of the input image in order to identify an initial result, then performing, on the initial result, one or more subsequent search operations that each use a longer or more complete version of the signature; wherein programmatically analyzing each of the plurality of images in order to determine the signature of the item includes: (i) programmatically determining a category of the item, (ii) based on the determined category, programmatically determining the one or more focus items within each image of the plurality of images, and (iii) determining the signature based, in part, on the focus item.