University of Toronto student Melissa Leggieri was on her way to class when she suddenly realized she was being watched.

Walking through Yonge-Dundas Square in Toronto, Ms. Leggieri looked up and saw herself broadcast on a massive digital billboard.

"I was shocked because I didn't realize what it was and I had no idea why I would be on it," she said, calling the realization "creepy."

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The billboard ad is part of a campaign launched last week for film distributor Elevation Pictures, to promote the new Oliver Stone movie about Edward Snowden, who leaked information about the U.S. National Security Agency's surveillance programs. Once Ms. Leggieri realized that the video was promoting the movie, her impression changed.

"I thought it was brilliant," she said. "It makes you realize that cameras could be anywhere and people could be watching and recording me, and I wouldn't know it. I'm not entirely caught up with the Snowden story, but I know he advocates for privacy ... it was perfect."

The campaign forced the Toronto ad agency that created it, DentsuBos, to grapple with privacy questions itself. It worked with advertising company Cieslok Media to install a security camera that would stream real-time video to one of its billboards in the square.

"We thought about what we were going to do; are we going to cross any lines," said Jon Freir, executive creative director at DentsuBos.

The campaign, which continues through this weekend, overlays animation on each video, which displays the co-ordinates of the square, with the words "tracking" and "target detected" appearing over footage of real people there.

Depending which way they are facing, people's faces may be visible, if too small to be distinctly identifiable.

"I would be gobsmacked if any other client or company wanted to film customers and put them on a screen," Mr. Freir said. "Because of the nature of the message with Snowden, it was right … What Snowden has been trying to do, we wanted to make people feel it. You can read about it, but until you actually feel it you don't internalize it – you intellectualize it. When people saw themselves [on the billboard] they got spooked … It feels very intrusive to people."

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It's undeniable that Mr. Snowden's revelations have contributed to a climate of increasing concerns over privacy, and not just in the U.S., where the leak occurred.

In Canada, nine out of 10 people reported concerns over whether their privacy is protected, according to a survey conducted in late 2014 for the Office of the Privacy Commissioner of Canada (OPC); 34 per cent said they were "extremely" concerned, an increase from 25 per cent who said the same in 2012.

The campaign also comes at a time when people's trust in advertising is in question, largely because of the marketing practice of tracking people's behaviour online in order to deliver "relevant" ads to them.

Consumers often do not have a grasp on what exactly companies know about them, or how to control the dispersal of their personal information. The same OPC report found that 80 per cent of those surveyed were "very" or "somewhat" concerned about marketing companies using their personal information to analyze their likes and dislikes.

In the U.S., 91 per cent of adults said that consumers have lost control over their own information, while 80 per cent of those who use social media were "concerned about third parties like advertisers or businesses accessing the data they share on these sites," according to a 2014 report, "Public Perceptions of Privacy and Security in the Post-Snowden Era," from the Pew Research Center.

This theme appeared in another ad campaign, launched last week. Ubisoft Entertainment SA is promoting its game Watch Dogs 2, the plot of which involves an evil electronics company selling "smart" objects such as connected TVs that learn viewers' habits and remotely controlled security systems. In a video ad, the fictional hacker group warns that the products are a smokescreen "designed to infiltrate the last refuge of your privacy" and encouraging players to visit a website that will help them join the "resistance" against the project.

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"Ever since Snowden's revelations, distrust is at an all-time high," said Ann Cavoukian, director of the Privacy and Big Data Institute at Ryerson University, and former privacy commissioner of Ontario. "If businesses develop a trusted relationship with customers, then customers are far more likely to want to provide information to those businesses. It's based on trust."

Ms. Cavoukian objects to the DentsuBos campaign, partly because there are no notifications posted in the area warning people that they are being filmed.

"They couldn't consent to participating in this," she said. ".What does privacy mean? It's all about personal control."

Could a side effect of the Snowden campaign be to raise further questions about trust in advertising, by creeping people out?

"That's one of the things we struggled with," Mr. Freir said. "We're getting all these new ways of targeting advertising and all these new questions are coming up. We're going to learn where the wrong turns are and the right turns, along the way."