Probably not a good idea to take the polices word for anything to do with the law ... especially with gems like:
The force said only police had the authority to investigate, solve and prosecute those responsible for crime.
Mind you, the whole article suffers from "crap jounalististis" - aka "BBC disease ..."
But Mr Callaghan said he was visited by police community support officers who said they were concerned about the posters.
Right, so now it's not "police" as such, but PCSOs - whose grasp of the law is likely to be less than razor-like.
... we go on:
"Police spoke to my staff saying it was a breach of the Data Protection Act. I was a bit shocked," he added.
Police ? or PCSOs ? They are two very distinct things (you'd think).
The BBC understands the images would not have breached data protection rules as they were owned by Mr Callaghan.
In which case the BBC understands incorrectly. Data protection has very little to do with the origins of the data, and a lot to do with who the data is about. It's very hard to breach data protection laws if the data is about an unnamed (and unknown) person. But even then, there are exemptions (and defences) that would apply for law enforcement and to protect existing rights (both of which seem the case here).
Incidentally, the police don't prosecute crime (unless the CPS has been abolished since Friday). With howlers like that, I would really rather wear a watch in Essex than ask a policeman the time.