Stand there, shut up, and look adoringly at the candidate. Susan Walsh, campaign organizer for 2 different parties, now a Humber professor of media studies, tells all. 6:50 Political hecklers usually shout out their opposition from the back of the crowd, so it came as a surprise this week when someone standing behind Stephen Harper, in support of the Conservative leader, was the one with the very loud voice.

The heckler wanted a reporter to "ask questions on the topic at hand," presumably hoping the media representative would not ask about the Mike Duffy trial, which has been the main focus of questions for Harper recently.

Harper appeared to take the distraction in stride, turning briefly, smiling, waving and saying "OK, OK."

But somewhere, there was most likely a campaign organizer thinking this was not OK. For the supporters who are assembled to stand or sit behind a leader at campaign stops, there are generally accepted guidelines. Speaking out is not one of them.

"You're supposed to look adoring and interested and clap at the appropriate times," says Susan Walsh, who has been a campaign organizer for the Progressive Conservatives and the Liberals in the past, and is a professor in the School of Media Studies and Information Technology at Humber College.

Otherwise, it's a pretty simple instruction for those invited to share the limelight: stay silent.

That backdrop of supporters' faces — "potted plants" as they are called by some observers, or "wallpaper" in Walsh's lexicon — has become a key component for campaigns trying to make that personal connections with voters in a world where TV and video images have taken on greater significance.

After a Tory campaign stop in Toronto Tuesday, a supporter fed up with questions about the Duffy trial hurls profanity at reporters 1:29 "Election campaigns in particular are about persuasion, and persuasion can happen visually or verbally," says Jonathan Rose, an expert in political communications and an associate professor in the department of political studies at Queen's University in Kingston, Ont.

"Often what gets reported are the things that are said, but the visuals are powerful rhetorical symbols of the kinds of messages that the party and the leader want to convey."

Nothing random

None of it happens by accident.

"You want to associate the people with what you're talking about and it humanizes the policy because you see who that policy is directed at," says Marcel Wieder, president and CEO of Aurora Strategy Group.

NDP Leader Tom Mulcair speaks at the launch of candidate Jennifer Hollett's Toronto campaign office on Aug. 6, 2015. (Cameron MacIntosh/CBC)

To this end, members of campaign advance teams work ahead, particularly for leaders' tours, scouting out possible locations for announcements, and determining whether they want or need people in the background for that appearance.

"If you put in people, then it … shows support, it humanizes the leader but it also gives you a slightly different look for every speech so not everything looks the same," says Walsh, who also works for Aurora Strategy Group.

Sometimes supporters volunteer without being asked.

"A lot of party members want to be in the backdrop," says Bruce Kyereh-Addo, who did advance work for Wild Rose Party Leader Danielle Smith in the 2012 Alberta provincial election campaign.

Lots of legwork

While some party supporters may make the initial approach, in other instances there is more legwork required of the advance team and campaign staff.

"This is something that a lot of people think is an easy job and it's really not," says Kyereh-Addo.

The makeup of the backdrop may also be influenced by the nature of the announcement the politician is making.

"Let's say it's a labour policy and you're an NDP campaign," says Wieder. That might entail talking "to some union- friendly groups to ask their members to come out to support it."

Or maybe the leader's advance team goes right to the local party.

"You may go straight to your own party base and say OK, the five ridings in this area, we need you to each supply 20 people that we can rely on, and then each campaign is going to say, OK 20 volunteers, here's where you need be," says Wieder, who has worked at federal, provincial and municipal levels, mainly with the Liberal party.

Campaigns also aim for diversity in the backdrop to reflect the Canadian population: faces of men and women, some older, some younger, along with ones of ethnic backgrounds.

How much support?

Hecklers love campaign rallies, both now and in the past. 1:11 "If the leader were surrounded by a background of homogeneous people or by no one, it would be a problem," says Rose.

"It would raise at some level, maybe not consciously, but at some level, questions about the degree of support the leader had."

Once the people are chosen, there's nothing random about where they are positioned in the backdrop.

Liberal Leader Justin Trudeau campaigns in Calgary on Aug. 3, 2015. (Todd Korol/Reuters)

"They will ask the people who come to come an hour ahead of time, and they will then figure out where everyone stands and they'll move people around so the short person is not being blocked by taller people, that there's not too much of one nationality on one side of the stage," says Wieder.

Instructions to the volunteers are most likely given verbally: look engaged, don't pull out your cellphone or a camera. A release may be signed giving the campaign permission to take the person's photo.

No detail is too small.

"If somebody's wearing body art, has tattoos, they may ask them to wear a long-sleeve shirt so that it doesn't show," says Wieder.

There's no monetary compensation for the person's time.

Just a handshake

"The greatest remuneration I have seen is either a handshake from the leader or a T-shirt," says Wieder.

As much as the backdrop of faces has become a campaign essential, determining its overall impact is a more elusive challenge.

"It's hard to say," says Rose. "It's only one element and it's a bit difficult to pull that thread and see how everything unravels."

Local workers flank Conservative Leader Stephen Harper during a campaign stop in Iqaluit. (Travis Burke/CBC)

"But at the same time it is a constant through the campaign. It is the way in which the media focuses and reports on the leaders' tours so in that sense it's very important."

Still, a cynic might see it all as a bit artificial and crafted, just as potted plants are arranged on a windowsill.

"It's a bit sad when we use voters and citizens as props in politics," notes Rose, "but that's really what they are and perhaps that speaks volumes about the nature of election campaigns and also the way that the campaigns are covered."

That said, it's unlikely the backdrop of faces is going to disappear from the campaign trail any time soon.

"It's a trend that has grown over the last 15 years," says Walsh. "I can't see it stopping soon partly because there are so many stops and it can all start to blend together. At least the faces make it a little different."