The paper deals with the problem of error estimation in 3D reconstruction. It shows how interval analysis can be used in this way for 3D vision applications. The description of an image point by an interval assumes an unknown but bounded localization. We present a new method based on interval analysis tools to propagate this bounded uncertainty. This way of computation can produce guaranteed results since a datum is not the most probabilistic value but an interval which contains the true value. We validate our method by computing a guaranteed model for a projective camera, and we achieve a guaranteed 3D reconstruction.