Anamorphoses are distorted images that need to be seen from a special point of view in order to reconstruct the correct image (perspectival anamorphosis). In catoptric anamorphoses, a mirror is used to restore the original image. We describe an effective procedure, using ray-tracing software, to define, test and build general catoptric anamorphoses. Users can define the mirror's shape, the surface on which the distorted image lays, and set the observer's point of view.The method can be used to virtually render and test anamorphoses designs or to output a distorted image in any suitable image format that can be printed at any scale, to obtain a real size version of the anamorphosis. We show examples with different mirrors and different distorted image surfaces.