Example of a complex lensed image system obtained from lensing by a composite mass distribution (Hernquist+gNFW) and well reproduced with a power-law mass distribution. Left: lensed image positions and critical curves for the fiducial composite model (light cyan) and for the power-law model (black). Right: corresponding caustics and source positions for the fiducial composite model (light orange) and for the power-law model (red). The small inset panel provides a zoom of the inner caustic.