V-band image of WFI 2033-4723 obtained by stacking the 14 best seeing and sky background images (V-band template image). The quasar and star, which we use both as a constant reference and PSF model, are labelled. The four lensed QSO components are enlarged in the darker box. The field size is 9.7 arcmin ×9.5 arcmin. The stamps used for the kernel computation are defined as 17-pixel squares (see Sect. 4).