  This paper gives a summary of the content-based Image Retrieval and
Content-based Audio Retrieval, which are two parts of the Content-based
Retrieval. Content-based Retrieval is the retrieval based on the features of
the content. Generally, it is a way to extract features of the media data and
find other data with the similar features from the database automatically.
Content-based Retrieval can not only work on discrete media like texts, but
also can be used on continuous media, such as video and audio.
