Detail (10′ × 10′) of three mock images created with SkyMaker from a z-band simulated catalogue obtained using the Stuff application. Images differ only in the FWHM of their adopted PSF: (a) 0.7, (b) 0.9, and (c) 1.1 arcseconds These images were used to study the behaviour of the SExtractor application to obtain photometric parameters, including PSF-model photometry, under controlled but conditions close to those of the images used for the assembly of the OTELO core catalogue. More details in text.