While pages on the Web contain more and more multimedia information, such as images, videos and audio, today search engines are mostly based on textual information. There is an emerging need of a new generation of search engines that try to exploit the full multimedia information present on the Web. The approach presented in this paper is based on a multimedia model intended to describe the various multimedia components, their structure and their relationships with a pre-defined taxonomy of concepts, in order to support the information retrieval process. A prototype of an image search engine, based on this approach, is presented as a first step in this direction, and results are discussed.