If they are doing it to try and persuade the OP to part with money, then, in my opinion, that's an offence under the 1981 forgery act, sections 1 and 3:
"1 The offence of forgery.
A person is guilty of forgery if he makes a false instrument, with the intention that he or another shall use it...
What I meant was, if the person who gets the ticket disputes it then it will go to a court (or tribunal). It is then that the photos will be presented as evidence.
Agreed though, it is very strange that a council would do something so obvious.
They aren't allowed to do that. What they can do is present it to a court and say "We believe this image shows the registration number xxx123" and let the court decide whether they agree. If they present, as evidence, what appears to be an altered photo the defence will have it thrown out.