Ed Miliband's advisers believe he has an image problem. With less than ten months to go until the general election, they have decided he can no longer ignore it and must tackle it head on.

"I am not from central casting," Miliband said today, telling his audience that "you can find people who are more square-jawed, more chiseled, look less like Wallace."

Like a bullied child who mocks himself before his tormentors get the chance, Miliband attempted to turn his biggest negative into his biggest positive.

But this was not just about self-deprecation. This was an attempt to turn the attack back on to David Cameron. Today he contrasted his own apparent inability to eat a bacon sandwich, with the cool ease with which David Cameron posed with huskies and solar panels. The point was that image is far less important than substance.

There are two obvious problems with this line of attack. The first is that Miliband himself is no stranger to the world of image management. It's all very well attacking Cameron's "photo-op politics" but not when Miliband himself has just returned from a trip to the US, the sole purpose of which was another photo opportunity. And Cameron may well be obsessed with his image, but it's hard to make that point when Miliband himiself is currently seeking a high profile new adviser to manage his own.

The second problem is that it is a line of attack that has been tested to destruction. Labour's 2010 general election campaign was based on the idea that while Cameron had the style, Gordon Brown had the substance. 'Not flash, just Gordon' was the slogan.

At the time this seemed like a viable line of attack and it probably did resonate with some voters. But it also failed to win Labour the election. In a choice between style and substance, voters chose style. Why does Miliband believe the result will be any different this time?

Miliband's attack is also a huge hostage to fortune. In the next nine months, he is likely to take part in dozens if not tens of dozens of photo-opportunities. At every one of these photo-opportunities, the press and his opponents will remind him of his words today.

None of this matters of course if Labour can successfully change public perceptions of Miliband. The Labour leader's dreadful opinion poll ratings are currently the biggest drag on Labour's chances of winning an overall majority at the next election. If Miliband's speech today is the beginning of a process to turn those ratings around, then it will all have been worth it.

This attempt may struggle however. Shortly after the speech ended, I was contacted by a TV producer asking me to come onto their programme to talk about "Ed Miliband's speech about being weird." This is precisely the problem. Rather than solve his image problem, Miliband may have simply reinforced it.

It's worth saying that this negative image is largely unfair. Having watched and spoken to Miliband at close quarters, I don't believe he is any more weird than any other frontline politician. He is from what I can tell, a decent man who looks and sounds pretty much how most politicians in Westminster look and sound.

Public perceptions on these matters are often far from reality in any case. Miliband is currently perceived as "weird" and "awkward" but this is not the impression most people get when they meet him. By contrast Boris Johnson is widely seen as human and personable, yet people who know him say he has few personal friends and apparently finds normal non-political conversation with others difficult.

Image does matter in politics, especially at a time when the public are so disconnected from it. But it is not the only thing that matters. The current generation of politicians were raised in the Blair years and so have come to believe that politicians must look or sound a certain way in order to be popular. This is a huge mistake. The most popular politicians in the country are not those who fit the "central casting" mould. Boris Johnson, Nigel Farage and even Alex Salmond would not be picked by any casting agency, but their personal ratings are far higher than any of the many politicians who would.

Miliband should relax. Image is not about fitting a certain mould, it is about how people perceive you. Miliband too often comes across as a man trying to sound like Tony Blair and look like David Cameron. He is neither of these things and should stop trying to be.

Miliband is a decent man with potentially popular policies, but too often this is lost in his attempts to look and sound just like the "central casting" politician he claims not to want to be. It is this basic inauthenticity which is the real source of his image problem.

Miliband is at his best when he is content just to be himself. His finest moment in recent times was his appearance on Desert Island Discs. Obstinately and at times painfully uncool, his selection was also incredibly endearing. How much better to have a leader who admits to liking A-ha and Neil Diamond, than to have a leader like David Cameron whose own selection was so obviously focus-grouped and inoffensive.

If today's speech was just another attempt to fit him into the mould of Cameron and Blair, then it will have been a failure. If it was a new attempt to 'let Miliband be Miliband' then it means Labour are finally on the right course.