BEIRUT (Reuters) - The first picture shows a crowd of thousands packed into a central square in the city of Isfahan this week for a speech by hardline cleric Ebrahim Raisi, the top challenger to President Hassan Rouhani in Friday’s Iranian presidential election.

Iranian youth use their mobile phones as they rest at a park in Tehran, Iran, May 16, 2017. REUTERS/TIMA

Immediately below is another picture of the same square, with a smaller crowd who had come out the previous day to see Rouhani, with red arrows pointing out the empty areas.

The contrasting photos have been posted on hardline social media sites and viewed by tens of thousands of people. Reuters cannot verify whether they give an accurate view of the true size of the crowds at the rival events. But they provide a fine example of how hardliners have caught up with reformers in using social media to spread their message.

With the Iranian presidential election only days away, both sides have launched a social media free-for-all unprecedented in Iranian political history.

Traditionally the reformist or moderate political camp has been the main user of social media in Iran. When security forces cracked down on protests after the disputed 2009 presidential election, thousands of young Iranians posted photos and videos on Twitter. Now, their opponents have got in on the act too.

“For the first time, the opponents of the reformists are also using social media,” said Saeed Leylaz, a Tehran-based economist and political analyst.

Iran has a young, tech-savvy population: approximately 60 percent of the population of 80 million is under 30.

“Social media has completely taken over the spreading of information and news about the election,” Leylaz said. “There’s no domestic or international media that has the same impact.”

By far the most popular social media outlet is Telegram, a chat service that is a niche player in most Western countries but has some 20 million users in Iran, according to a report by the Iranian Students’ News Agency (ISNA).

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Telegram allows users to set up “channels” to broadcast pictures, videos and other messages to a wide following. For Iranian reformers in particular, that offers a way to get out messages that otherwise would be thwarted by censorship.

They used it this week to share a message from former President Mohammad Khatami appealing to voters to come out in force and cast their ballots for Rouhani: it is illegal in Iran to show pictures of Khatami or name him on TV or in newspapers.

“We will vote for Rouhani for freedom of thought, logic in dialogue, law in practice, advocacy for citizen’s rights, and for bringing social and economic justice to our society,” Khatami said in the message. “This time it’s you who must repeat it.”

“ALTERNATIVE FACTS”

But conservatives have discovered social media’s power too. Hardline outlets have shared video footage of angry coalminers pounding on Rouhani’s car in protest during a visit to a mine where dozens had been killed in an accident.

Opponents have posted documents on social media sites which they say show the president taking part in corrupt real estate deals. Rouhani has denied allegations of corruption repeatedly.

“Seldom before have the candidates employed social media to reveal documents aimed at sabotaging their rival’s campaign,” said Ali Vaez, senior Iran analyst at the International Crisis Group. “Negative ads and alternative facts are spreading like wildfire on social media in this election.”

During a TV debate last week, Tehran Mayor Mohammad Baqer Qalibaf, a conservative candidate who subsequently quit the race to endorse Raisi, announced he would post documents about his own income on Telegram to show that he is not corrupt.

“The opponents of the government have benefited from social media,” said Shahrouz Afkhami, a former parliamentarian who served on a committee examining social issues.

But even if the hardline faction is now getting better at using it, security forces like the powerful Revolutionary Guards still mainly view social media as a threat.

In mid-March, a dozen administrators of reformist channels on Telegram were arrested by the Guards, according to human rights groups. In late April, the Iranian judiciary blocked the live voice call service offered by Telegram, despite attempts by Rouhani to keep the service available.

“We emphasized that starting the voice call service of Telegram will result in us not being able to control anything,” the deputy head of the intelligence wing of the Guards, Hussein Nejat, said after the service was blocked, according to the Iranian Students’ News Agency.

“But the president answered why do you oppose any technology that comes from the West?”

Nejat announced in late February that 157 obscene Telegram channels had been “crushed,” according to the Tasnim news site.

“The security services of the Islamic Republic don’t like things they can’t control,” said Roozbeh Mirebrahimi, an Iranian journalist and blogger who worked for a number of reformist dailies and now lives in New York.

“There are millions of Telegram users in Iran. How can you control it? Unless you shut it down completely. This is a fight that has been around and will continue to be around.”

Mirebrahimi noted that in their social media personas, both factions - reformers and hardliners alike - share a sharp sense of humor and distinctive satirical tone.

“You can see this culture of jokes in the social media of both sides,” said Mirebrahimi. “They are from the same society after all.”