1. A method for searching a repository of documents using an image as a search query, the method comprising: receiving a query image I* to be used to search a repository of documents; hashing said query image to obtain a hash value h(I*) for said query image; setting an initial threshold level τ 0 for said search; performing a no-reference quality assessment on said query image to estimate of a measure of quality Q(I*) for said query image e; adjusting said initial threshold level by said measure of quality, said adjusted threshold defining a possible match for said search; for each current document in said repository: for each current image in said document: extracting said current image I (k) from said current document; hashing said extracted current image to obtain a hash value h(I (k ) for said extracted current image; computing a distance between said hash value h(l*) of said query image and said hash value h(I (k ) of said extracted current image; comparing said computed distance against said adjusted threshold; and flagging said current document as a possible match in response to said computed distance being less than said adjusted threshold; and providing any of said flagged documents to a user in response to said search.