The Supreme Court of Canada will rule Thursday morning on the case of a high school teacher who was acquitted after he was caught filming female students' chests with a camera pen — a decision that could have a profound impact on privacy rights in this country.

At issue is whether the female students — 27 youths aged 14 to 18 — had a reasonable expectation of privacy when they were being secretly recorded on school grounds.

Back in 2015, the original trial judge determined that London, Ont. teacher Ryan Jarvis had violated the students' privacy by using a so-called spy pen to secretly record their chests and cleavage, calling his behaviour "morally repugnant and professionally objectionable."

But Justice Andrew Goodman wasn't satisfied the videos were filmed for a sexual purpose and acquitted Jarvis.

The Ontario Court of Appeal went another way.

Most of the judges on that bench ruled that Jarvis did act with sexual intent but still upheld his acquittal, arguing the students had no reasonable expectation of privacy at school. The court pointed to the presence of 24-hour surveillance security cameras in and around the school "which were clearly visible to everyone."

Gillian Hnatiw, vice-chair of the Women's Legal Education and Action Fund, says she is optimistic the Supreme Court's judgement will protect individuals' privacy interests. (Graeme Roy/Canadian Press)

The Supreme Court is looking into whether the Court of Appeal erred in its conclusions and will release its decision around 9:45 a.m. ET Thursday.

Arguments 'take women back three decades'

Ontario's Information and Privacy Commissioner Brian Beamish called the lower court's ruling "unacceptable."

"I still think there are social norms at play here. I think most people still would find it unacceptable for someone to be filming an individual without their permission on a public street. That cuts against what we feel is acceptable behavior," he said in an interview with CBC News Wednesday.

His office is one of a handful of groups that have intervened in this case, arguing for a reversal.

While he acknowledged the concept of public spaces is changing with the spread of surveillance cameras, Beamish said people don't completely surrender their right to privacy when they venture into a public space.

The way this court grapples with the notion of privacy in public spaces will likely have profound implications for the ability of Canadians to protect themselves from harmful and unwanted surveillance. - Counsel for the federal privacy commissioner

"We thought there was a really important privacy principle at work here, and that is we do not give up all our expectation of privacy even though we may be in a public or semi-public space," he said.

"There are ... and there must be, reasonable limits on intrusion."

Lawyers for the federal privacy commissioner, another intervener, declined to be interviewed, but their submission argues that this case is important "to the future of privacy rights in Canada."

"In an era where technology increasingly allows for the surreptitious observation and recording of individuals through devices such as drones, body-worn cameras and ever-ubiquitous smartphones, the way this court grapples with the notion of privacy in public spaces will likely have profound implications for the ability of Canadians to protect themselves from harmful and unwanted surveillance," says their factum filed with the Supreme Court.

Brian Beamish is the the information and privacy commissioner of Ontario. (CBC)

For lawyer Gillian Hnatiw, vice-chair on the Women's Legal Education and Action Fund board, the case marks the return of arguments she's fought against in sexual assault and harassment cases for years.

"I can't believe that we're having this conversation again," she told CBC News. "We are at a new frontier of sexual crimes and we seem to have gone back to the original analysis, which is, 'Well, where was she and what was she wearing?'

"To suggest that simply by going into a high school in a shirt that will enable a teacher to stand above you with a pen light and secretly film your cleavage ... (it would take) women back three decades and put the onus back on them to ... essentially withdraw from the public sphere in order to protect themselves."

Hnatiw said she's optimistic the Supreme Court's judgment will protect individuals' privacy interests.

"I think it's a perverse outcome if Ryan Jarvis has a greater right to privacy in his pen cam, and the images on that pen cam, than the women who are the subject of those images have in their own bodies."

No matter where the Supreme Court justices land, it will mean the Ontario Teachers' College can move ahead with a separate disciplinary hearing.

"When we get the decision we'll know two things — first of all (whether) Mr. Jarvis been found guilty of this criminal offence. And we'll also have better guidance on what is the expectation of privacy within a school setting," said the college's legal counsel Caroline Zayid.

"I think we recognize that the question of intruding on students' privacy generally is changing. It's not just physical searches anymore, but those electronic searches or remote observations and recording are much more of a concern for all Canadians."

Jarvis's lawyers said they won't be commenting before the judgment.