Jennifer Pawluck was charged in 2013 after snapping a photo of graffiti, which she didn't draw, and uploading it to Instagram, a photo-sharing social media site.
Quebec court Judge Marie-Josee Di Lallo said she had no doubt the criteria necessary to find Pawluck guilty of harassment had been met.
The judge also made it clear that online behaviour can have repercussions.
"We must be conscious that a simple click from a smartphone or computer, that takes just a fraction of a second, can have serious consequences," Di Lallo said. "At a time when social media is taking more and more place in our lives, we must be even more vigilant."
Cmdr. Ian Lafreniere, one of the city's most visible police officers and the man whose face was on the graffiti, told Pawluck's trial the image shook him up, scared his children and caused his wife to stop working for several months.
Pawluck, now 22, testified in late February she posted the snap without even knowing who Lafreniere was. She conceded the image was not "peaceful" in nature but that she'd sent it as a statement against police in general — not one officer in particular.
The judge expressed skepticism about Pawluck's claim on the identity issue, given her involvement as an activist during student demonstrations in 2012.
Lafreniere is the main voice of the police force during major events and was very visible on TV during the highly charged student protests, which featured numerous clashes between authorities and demonstrators.
His name was scrawled on the graffiti and his name spelled two different ways was among the hashtags added by Pawluck, including an anti-police tag #acab — which stands for all cops are bastards.
The judge said she felt the evidence presented was sufficient.
"Seeing your face drawn, with a bullet in the head, one cannot help but feel threatened," Di Lallo said. "And this, even if you're a police officer."
A smirking Pawluck left the courthouse repeating ''no comment'' as a friend shielded her from cameras. Her lawyer, Valerie De Guise, also declined to speak.
Pawluck was charged under a summary offence, meaning the maximum sentence is six months in jail or a $5,000 fine. Sentencing arguments will take place May 14.
Following her April 2013 arrest, there was intense debate online over whether a criminal charge was necessary in such circumstances. Thursday's guilty verdict reignited that debate.
Prosecutor Josiane Laplante said the question of freedom of expression did not come up during the short trial, which focused strictly on the harassment issue.
Laplante hopes the case will result in increased online prudence.
"I think it's very important to think of the impact we have when we put something on the Internet, the impact on other people when we post something," Laplante said.
Lafreniere told The Canadian Press he wouldn't comment for the time being.
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