Police forces which "name and shame" criminals must remove the details from their websites after a month, according to new rules released today.
Criminals' personal details, such as their name, age, where they are from and their offence, should be published routinely, the Ministry of Justice said.
But officers will need a specific reason to publish photographs. The detailed rules state there should be a "presumption" in favour of making public case information from the Crown and Magistrates' Courts.
But data protection and human rights laws mean there are restrictions on what is published, how it is made public and for how long.
Police and town halls should take into account the impact of publishing on the offenders' family, the guidance says.
Officials should also consider whether it is "proportionate" to make the verdicts and sentences public and whether publishing personal details could have an "unjustifiably adverse effect" on the criminal.
They can consider saying just that "someone" has been convicted of a crime without revealing the specific details of who, if that is enough to reassure the public.
With minor crimes they can say only the number committed and how many were dealt with and not publish any more details.
Fears about the long term "adverse consequences" of publication on criminals mean the data might be limited to people who live near where the crime is committed.
Instead of putting it on the web, forces can hand out leaflets or make information available at public meetings, the guidance says.
"Online publicity needs to be justified, and will not usually be appropriate for minor offences/sentences or for first time offenders," the document states.
Shadow justice secretary Dominic Grieve said: "This is too little, too late.
"We have long called for new rules to make it crystal clear that public protection - for police, prison and probation officers - comes before the privacy of criminals.
"That guidance should be clear and user-friendly for those on the frontline charged with protecting the public, not vague and riddled with uncertainty."
Justice Secretary Jack Straw said: "If people are to have confidence in our criminal justice system, justice must be done - and be seen to be done.
"Individual crimes often get a lot of media coverage and news can spread across communities quickly that a crime has been committed.
"However, the news that someone has been caught, prosecuted, convicted and sentenced does not travel as far.
"This guidance explains, once and for all, that authorities can publish the details of crimes and the punishments criminals have received, and that the Government actively encourages them to do so.
"It is vital people know that criminals will not escape the consequences of their crimes."
Later, the Ministry of Justice said the guidance was a "first step" and would be kept under review - including the one month time limit.
A spokesman said: "We will closely monitor how the guidance works. It is a first step towards routinely making criminal convictions public so that communities can see that justice is being done.
"The length of time that offenders' details should remain online is one aspect of the guidance that will be kept under constant review. If it emerges that changes are needed, we will make them."Reuse content