Illustration of persistence in the stack of our data. Left: stack made without masking the persistent images (i.e. fake sources) in the individual images. Right: stack made with masking. The circles mark the predicted locations of persistent images in the stack, see text. The circles are labelled with the J-band Vega magnitude of the star that caused the persistence in question. The diameter of the circles is 15′′. North is up and east is left