Photos are not a legal requirement within the regulations under the Traffic Management Act; essentially it is who the adjudicator believes based on the civil law test of "on the balance of probabilities". Of course, nowadays, councils get their CEOs to take photos and these are normally viewable on their webpages on quotation of the PCN Number and the car registration mark.
Here I think that balance lies on the council side. Why ? Because the location shown on GSV is of a clearly marked bay, with a sign at one end saying "Resident permit holders only, Mon-Fri 8.30am to 6.30pm. Even if you parked right at the other end of the bay you are under a duty as a motorist parking there, to determine what, if any, restrictions apply to that bay.
https://maps.app.goo.gl/QtEUh7FfH6AFGBep6Having said all the above, I suggest you submit representations on a non-confrontational basis asking for mitigation, based on both you and your companion not visiting Westminster very often, and didn't realise that BBs were not valide for use in their resident bays. You may get lucky, you may not.