When Rupert Murdoch radically changed his Twitter photograph last week it was a signal of how seriously he was taking his new experiment on the social networking platform. Gone was the amateur shot that appeared to have been taken on his phone, showing him craggy faced, chewing his lip and wearing a sweater. In its place was a professionally taken portrait of a switched-on businessman in a shirt and tie.

The initial assumption had been that this Twitter experiment was a PR exercise, an attempt to soften Rupert's image after a humble pie year in which his personal reputation has faced an onslaught unparalleled even in his own extraordinary saga. But in the space of a few days he appears to have been convinced of the power of the free online medium and rethought his strategy.

Having opened his account with comments about his holidays ("great time in sea with young daughters, uboating") and praising his Fox film empire for the movies he was enjoying, he hardened his tone to talk about business and politics. In particular, he has used the platform for endorsing his favourite politicians, such as Michael Bloomberg and, most significantly, Republican presidential hopeful Rick Santorum ("only candidate with genuine big vision for country").

After initial amusement, Murdoch's every tweet provokes a flurry of analysis and brings thousands of new followers. Emily Bell, the former Guardian journalist who is head of digital journalism at Columbia University, tweeted: "If @rupertmurdoch can endorse Rick Santorum with 140 characters on a free platform, not sure why he needs expensive newspapers anymore".

The same thought must have occurred to some of those at News International where Murdoch's British newspapers are trying to build a digital audience behind a paywall. It's little surprise that Wapping journalists such as Danny Finkelstein, Janice Turner, Caitlin Moran and David Wooding quickly became part of Rupert's 119,000 Twitter following.

"There's a certain irony to the fact that whatever the message he is trying to convey he is using Twitter to do it, a free media platform, when he has put much of his businesses' political content behind a paywall," says Stewart Easterbrook, CEO of media agency Starcom MediaVest Group. "When push comes to shove people revert to the most effective, most immediate media opportunities."

A source close to the News International paywall strategy acknowledged the irony of Mr Murdoch's "late conversion" to using social media, given that he paid $580m (£276m) for MySpace in 2005 and then sold it last year for $35m. "If he had this Damascene conversion five years ago he might have understood how to make money out of MySpace," he said. "But if the knockers are saying he's going to drop his paywall strategy, I would not go along with that."

But Michael Wolff, Murdoch's biographer, is a long-time doubter that the News Corp chairman, who is two months from his 81st birthday, will ever understand online media. "I find it really hard to imagine that Rupert is doing this unassisted," he says.

Not that he is convinced this is a heavily orchestrated News Corp play, quite the opposite. He claims that the great media titan is now a marginalised figure, under pressure to cede power and delegate decisions to colleagues and his children. "Rupert is increasingly uncomfortable within his own corporation," says Wolff. "Twitter could be a kind of outlet for Murdoch's own frustrations." The paywall strategists at Wapping may be hoping it's nothing more than that.

i.burrell@independent.co.uk