As more Canadian cities explore the use of body-worn cameras on police officers, questions are being raised over privacy rights and their effectiveness.

Support for the cameras across North America gained traction following the controversial deaths of several African Americans at the hands of police. In July, a white New York police officer was captured on camera applying a chokehold that led to the death of Eric Garner, who was unarmed. And in August, a white police officer in Ferguson, Mo. fatally shot unarmed teen Michael Brown.

Grand juries in the U.S. decided against indicting the officers in both cases.

Proponents say that body-worn cameras on frontline officers could help rein in incidents of excessive force and improve relations between law enforcement and civilians.

A study conducted by the University of Cambridge found that after body cameras were introduced by a police department in Rialto, Calif. complaints against officers dropped by 89 per cent. It also found that the cameras were possibly responsible for cutting down on misbehaviour on the part of both the public and the police.

Toronto police are planning to roll out body cameras for several units, including the city's TAVIS Rapid Response Team, sometime in early 2015.

The one-year trial was recommended as part of the PACER report, which was commissioned in response to a public outcry after the death of Sammy Yatim. The 18-year-old was shot and killed by a police officer in downtown Toronto in July 2013.

Toronto Const. James Forcillo has been charged with second-degree murder and attempted murder in connection with Yatim’s death.

Toronto Police said late last year that they believe the use of body-worn cameras will alter interactions between police officers and the public, since both parties will be aware that their actions are being recorded.

In Calgary, police deployed 50 cameras three years ago. A year later, the program was expanded to include all uniformed officers. Thirty videos captured by Calgary police in 2013 were used as evidence in court cases.

A special legislative committee in B.C. has also recommended that body-worn cameras be adopted across the province.

"It gives you the evidence you need; should something go horribly wrong, should there be challenges about the actions that the police have chosen to take," said B.C. MLA Spencer Chandra Herbert.

But critics have questioned whether the devices can cut down on incidents of excessive use of force, and whether recordings can help bring guilty parties to justice.

The mother of Eric Garner has pointed out that a bystander filmed the death of her son, and the actions of New York police officer Daniel Pantaleo, who placed her son in a chokehold.

"I mean, they had a video that represents a body camera – it did nothing," said Gwen Carr, Eric Garner's mother.

There are also concerns surrounding the potential for violations of people's privacy rights.

B.C.'s privacy commissioner, Elizabeth Denham, said last week that the devices are a "game-changers," and that there needs to be "careful" and "clear" rules about when the cameras will be turned on, and how long the records will be retained.

The federal privacy commissioner, Daniel Therrien, has also warned that expectations need to be kept in check. Therrien told The Canadian Press last month that there need to be rules regulating camera use and that recordings of innocent bystanders and innocuous interactions need to be kept to a minimum.

"There are clearly benefits to the use of body-worn cameras; however, there are also significant privacy implications," said Therrien.

Canada's former information and privacy commissioner, Ann Cavoukian, agrees. She says that as long as the privacy rights of Canadians are protected, body-worn cameras could prove to be a useful tool.

"If we could just pursue privacy and public safety related activities together – instead of as opposed to another – I think we will be advancing societal interests greatly," Cavoukian said.

In addition to Toronto, police departments in Vancouver, Edmonton, Montreal and Calgary have all initiated pilot projects to assess the use of the small lapel cameras on policing.

And in the U.S., officers from one of every six departments are now sporting the devices.

"Body cameras are going to be on just about every officer in the next few years," said Heath Bideau, a sales manager at Digital Ally, which produces body-worn cameras.

With a report from CTV Toronto's Scott Laurie and files from The Canadian Press