As Firstandbest says, privacy is not an issue as long as the photo has not been taken from private land (e.g. a garage forecourt). Also, as pepper points out, he does own the copyright to the photos. But . . .
There are three issues here, all of which could, if things went wrong, impact either on us as classic car owners or on the Forum.
(i) The owner of this "interesting" R4 suddenly gets a knock on the door. DVLA have already seen the photos and discussion and have decided to act.
The owner finds out about this Thread and vents his displeasure either on pepper or on Malcolm/Steven.
(ii) You've probably noticed that lots of cars on eBay have the numberplates hidden, presumably to prevent the car being stolen off the driveway.
There was a sad post about nine months ago from someone whose 1968 R4 had been stolen from a lock-up. To my mind this must have been a targeted theft - no-one would steal a 1968 R4 on spec - it would only be worth about £70 scrap value and if they wanted to use it as a joyriding car they probably couldn't even work out how to put it in gear. To a collector, however, it might be worth £2000 (more if concours).
As a result of the photos on this Thread, someone decides to steal the "interesting" R4.
Anyone posting photos of other people's cars might like to imagine themselves in the position of the owners in (i) or (ii). The fact that there was no legal right to privacy or that the photographer had copyright of the images would not be much consolation to them.
(iii) If DVLA were to read this Thread they might get the impression that the Historic Vehicle Exemption was subject to abuse. If they did, one can be sure that any changes made would not be to our (enthusiasts') advantage.