The Electoral Commission fears the craze for taking self-portraits on phones and posting them on social media threatens the secrecy of the ballot. However, taking photos is not against the law.
Anyone who inadvertently reveals how someone else votes in tomorrow's local and European elections could face a 5,000 pound fine or six months in prison.
"We have told staff that if they see anyone taking a photograph they should ask the person to delete it but not try to wrestle the phone out of their hands," said an electoral services manager at an East of England local authority. It would depend on exactly what they were taking a photograph of. We have told them to take a note of the names and addresses of anyone doing it. But we would not necessarily call the police," the BBC quoted the official as saying.
She said staff would also make sure polling booths had open backs so they could see what was happening - and had been told to put up "no photography" signs outside and inside the polling station.
Some have also received training in what a selfie is - and what to do when they spot someone about to take one in or around a polling booth.
There are elections across the UK to the European Parliament on Thursday and elections to 161 councils in England and 11 in Northern Ireland.
Under the Representation of the People's Act it is a criminal offence to communicate information about the way someone has voted or is about to vote - or to communicate the unique identification number on the ballot paper.
The Electoral Commission fears people taking selfies could accidentally reveal details about how they, or someone else, has voted, potentially putting them in breach of the Act.
But John Turner, chief executive of the Association of Electoral Administrators, said the law was not clear and needed to be updated for the 21st Century. "There is not an Act of Parliament that says you should not take a selfie inside a polling station," he told BBC News.
"This is essentially a piece of Victorian legislation and they didn't have mobile phones back then."
The Law Commission said it was reviewing all legislation on the way elections are conducted, including rules about secrecy and whether photography should be allowed, with a view to simplifying and updating them.