Overview of the strong lensing system of Abell 611. The knots that we used as constraints are marked as red crosses on the F606W ACS/HST image; enlarged images are shown in Fig. A.1. The magenta crosses indicate the perturber galaxies that were optimised singularly (see Case 6 in Table 5). The blue crosses correspond to a likely lensed system, identified by R09, which is not yet confirmed spectroscopically. We discuss our selection of the input images and its effect on the results in Sect. 3.2 and Sect. 3.7. The coordinates of all the systems are listed in Table A.1. The size of the field of view is  ≃ 50 × 42.5 arcsec; the image was smoothed with a 2 pixel FWHM Gaussian filter (1 pixel = 0.05 arcsec).