Is it a crime to take pictures?
It permits the arrest of anyone found "eliciting, publishing or communicating information" relating to members of the armed forces, intelligence services and police officers, which is "likely to be useful to a person committing or preparing an act of terrorism".
That means anyone taking a picture of one of those people could face a fine or a prison sentence of up to 10 years, if a link to terrorism is proved.
The law has angered photographers, both professional and amateur, who fear it could exacerbate the harassment they already sometimes face.
On Monday, a group is gathering outside New Scotland Yard for a "mass picture-taking session" in protest.
The event is organised by the National Union of Journalists. It insists the right to take pictures in public places is "a precious freedom" that must be safeguarded.
NUJ organiser John Toner said: "Police officers are in news pictures at all sorts of events – football matches, carnivals, state processions – so the union wants to make it clear that taking their pictures is not the act of a criminal."
The problems we can see arising are with junior officers using the legislation to overcome situations they find uncomfortable
British Press Photographers’ Association
The British Journal of Photography recently reported an incident involving a photographer in Cleveland who was stopped by a police officer while taking pictures of ships.
He was asked if he was connected to terrorism, which he wasn’t, and told his details would be kept on file.
A Cleveland police spokeswoman told the journal that "in order to verify a person’s actions as being entirely innocent," anyone in "suspicious circumstances" could be asked to explain themselves.
Photojournalist Marc Vallée is among those angry at the law. He specialises in covering protests and fears for the implications of Section 76.
"Alarm bells really are ringing," he told the BBC News website.
"I know some of it sounds a bit funny. Train spotters being stopped for taking pictures, that sort of thing, but I’ve spoken to people who’ve been on their own, at night and they’re surrounded by several officers. It can be intimidating.
"It may be that officers are just doing their best with a bad law, but if that’s the case, they need guidance to tell them, ‘Stop harassing photographers.’"
Mr Vallée also pointed out that members of the Royal Family were part of the Armed Forces.
"Are we going to be stopped from photographing them?" he said.
Photographers say they are frequently being stopped and searched
The NUJ said some police officers wrongly believed they had the right to delete photographers’ images.
Other critics, meanwhile, fear the new law could inhibit their right to peaceful, democratic protest.
Leo Murray is a spokesman for climate change campaign group Plane Stupid. His members film any direct action they take.
"It’s outrageous," he told the BBC News website. "It’s yet another in a long line of measures designed to erode people’s civil liberties.
"Being able to film the police has completely changed the way they are able to police our protests. It’s made us much, much safer and the risks of a violent confrontation have almost disappeared.
"If we couldn’t film they could act with impunity, they could just mete out violence with the confidence that nobody would find out.
"There’s absolutely no way we are going to observe this ban. If they try to bring charges against us we will fight them in the courts."
In a statement, Number 10 said that while there were no legal restrictions on taking pictures in public places, "the law applies to photographers as it does to anybody else".
"So there may be situations in which the taking of photographs may cause or lead to public order situations, inflame an already tense situation, or raise security considerations," it said.
Photographers could therefore be asked to "move on" for the safety of themselves or others.
"Each situation will be different and it would be an operational matter for the police officer concerned as to what action should be taken," the statement added.
This discretion, however, is what some feel is the key problem with the law.
Critics fear the new law could stop them photographing legitimate protests
Neil Turner, vice chairman of the British Press Photographers’ Association, said he believed there was no intention among senior ranks of the police to prevent legitimate photography.
"The problems that we can see arising are with junior officers using the legislation to overcome situations that they find uncomfortable or where they make judgements about photography and don’t know how to apply the legislation on the ground," he said.
"We firmly expect that there will be inappropriate uses of the act and that someone will end up in front of a judge before there is some clarity and before the purpose of the act is properly defined."
The Metropolitan Police insisted the law was intended to protect counter-terrorism officers and any prosecution would have to be in the public interest.
"For the offence to be committed, the information would have to raise a reasonable suspicion that it was intended to be used to provide practical assistance to terrorists," it said.
"Taking photographs of police officers would not, except in very exceptional circumstances, be caught by this offence."