Methods for retrieving images from a database are provided. A query image is obtained. A plurality of patches are extracted from the query image. A set of weightings is obtained according to a plurality of bases of a sparsity-based dictionary. The set of weightings includes a plurality of non-zero weightings. The patches are encoded with the set of weightings to obtain an encoding matrix. The database is searched based on the encoding matrix to retrieve the images corresponding to the query image. The database and the dictionary are dynamically updated to adapt to the query image encountered.