Without showing dates and location, that picture is as useful as poke in the arm with a sharp stick. Please repost showing all dates and the location.
Have you tried Plan A yet? A complaint to the landowner/managing agent/supermarket where the driver was a patron?
However, the NtK is not PoFA compliant and so only the unknown driver can be liable for the charge, as long as the known keeper doesn't blab the unknown drivers identity, inadvertently or otherwise.
This can be killed off with the following appeal as the keeper and if not, POPLA will likely cancel it.
I appeal as keeper. I am not obliged to identify the driver and I decline to do so. You are unable to transfer the driver’s liability (if any) to me because you have not issued a Notice to Keeper (NtK) that complies with the requirements of Schedule 4 to the Protection of Freedoms Act 2012 (PoFA) and it is now too late for you to do so.
The registered keeper cannot be presumed or inferred to have been the driver, nor pursued under some twisted interpretation of the law of agency. Your NtK can only hold the driver liable. Horizon have no hope at POPLA, so you are urged to save us both a complete waste of time and cancel the PCN or waste your money and issue a POPLA code so they can order you to cancel it.