We are developing an assistant robot system for administration of a library. In this system, an autonomous mobile robot obtains images with a camera, and composes seamless and high-resolution images of a bookshelf by using mosaicing and super-resolution techniques. In this paper, we propose a control method for the robot in front of a bookshelf as a part of this system. To obtain images that are suitable for mosaicing, a robot should take images from the same distance and orientation to a bookshelf. Our control method utilizes horizontal edges, which are detected easily in any bookshelf. The robot modifies its orientation with the edge in camera images. We implemented a super-resolution and mosaicing algorithm. Our implementation is simple. However, it can compose a high quality image in an experiment, since the robot obtains preferable images for the image processing.