1. A document and/or image retrieval method for retrieving a document and/or image corresponding to a captured digital image from a database by comparing features calculated based on feature points of the captured digital image with features calculated based on feature points of each of documents and/or images stored in the database, the method comprising: extracting the feature points from the captured digital image; defining a local set of feature points for each of the extracted feature points; selecting subsets of feature points from the defined local set; determining invariant values as values characterizing each selected subset for combinations of the feature points in the subset, the invariant values being invariant to a geometric transformation; calculating a feature by combining the determined invariant values; and performing a voting process on the documents and/or images in the database based on the preliminarily calculated features of the documents and/or images; so that the document and/or image corresponding to the captured digital image is retrieved from the database.