There is large amount of digital data floating all over the world today. If we want to search a particular image or file, we get a lot of results. CBIR are the systems which search an image or article on the bases of their content. Therefore, Content-based image retrieval has become one of the most active research areas from last few years. This paper gives a review of features used in content based image retrieval, a general model for CBIR and its applications.