With the rapid popularization of digital cameras and mobile phone cameras, we have witnessed an explosive growth in the size of digital image collections. Image retrieval, which is an area of the study concerned with searching and browsing images from a large-scale image database, has attracted much attention among researchers in the fields of image processing, computer vision, and database management both from the academia and industry during the last decades. In this book, we will show the problems of this area and discuss the possible solutions to these problems.