Details of the images used as constraints for the lens optimisation corresponding to the sources A and B (see Table A.1). The first three panels on the left show the location of the knots selected along the tangential arc, while the last four panels on the right show the conjugate knots identified in the quintuplet system. All panels were selected in the galaxy-subtracted image, obtained through the two-dimensional fitting algorithm GALFIT (Peng et al. 2002). The images were smoothed with a 2 pixel FWHM Gaussian filter for a better visualisation.