This paper illustrates the cooperation between Image Processing and Computer Graphics. We present a new method for computing realistic 3D images of buildings or of complex objects from a set of real images and from the 3D model of the corresponding real scene. We show also how to remove the real shadows from these images and how to simulate new lighting. Our system can be used to generate synthetic images, with total control over the position of the camera, over the features of the optical system and over the solar lighting. We propose several methods for avoiding most of the artifacts that could be produced by a direct application of our approach. Finally, we propose a general scheme where these images are used to test Image Processing algorithms; a long time before that the first physical prototype is built.