They've probably got high definition images.
Photos of work we do on the railway can be zoomed in on to check for quality, these are images sent via WhatsApp to work groups that supervisors and managers etc can check for quality/errors by zooming in on their lovely desktop computers. You'd hope with the billions involved in football the quality was up to scratch.
As for grainy images, close calls and incidents caught on train cameras and reported have really high quality stills and video footage, the stuff they screenshot or the video clips they release always seem to be low quality, perhaps trying to lul track workers into a false sense of security by making them believe they can't identify individuals caught doing wrong, but the cameras on the trains are top notch!!