Groucho Marx once said that the key to success in life is sincerity, and, he added, if you can fake that you have really got it made. Dozens of institutions - and not only political parties - have taken him at his word. Where we once had a trickle of brochures, glossy adverts and videos proclaiming their virtues, we now have a flood. Today, universities and schools, too, obsessively search for an attractive image.
The clients of PR - and their critics - begin by assuming that image is skin-deep, that you can buy it from the experts, like a new computer system or a fleet of cars. But one of the lessons of recent years, and indeed of the this election campaign, is that images are not as simple as that.
For a start, images are indivisible. For political parties, the behaviour of MPs influences whether or not people trust, say, the health policies. If you are a university, you may spend millions on award-winning buildings, yet it will be one sexually harassing lecturer that will stick in the public mind.
In the past reputations were solid, slow-moving, built of granite. Today, they are ephemeral and vulnerable, as our Prime Minister learned when his party's traditional reputation for economic competence disappeared in a single day. On Black Wednesday, for the first time, the Conservatives (unlike Labour) were associated with a big, public economic reversal.
The second lesson is if you want to change your image, getting a new logo will not take you very far. You need to think about what you are, what you stand for, what makes you different. The Labour Party learned this, the hard way, when all of its PR overhauls in the 1980s failed to translate into public trust.
When sensible organisations want to change their identity, they now like to use games, asking their managers to imagine what kind of car, sandwich or film their institution would be (and, yes, people are paid large sums of money to encourage grown men and women to do this). The key stakeholders are asked to think about their values, what motivates them to get up in the morning. Finally, at least in theory, what was once a disparate group of individuals discovers its shared sense of mission - an identity they can buy into. Then and only then, is it worth thinking up the flashy visuals.
This link between ethos and identity matters because if you do not achieve it there will be a dissonance between your brochure and how your staff behave.
The third lesson is that images are now global. A century ago very few institutions - excepting perhaps the big churches, the armed forces, and scientific societies - had to think too hard about their image around the world.
Today, everyone from the BBC to the Royal Family, and from Oxbridge to a small university, has to worry about this; for one thing, in the age of the Internet, bad news travels fast. Just as Shell's behaviour in Nigeria catapulted to Britain, so could damaging information about a British university's recruitment drive in Malaysia, wing its way back here.
Not much of this is under anyone's control. Big organisations cannot control what everybody in them says or does. So, there is a paradox - that, in an age of images, image may matter less than it used to.
The best any group can do is concentrate on doing well what it is already good at, and react quickly if things go wrong. Indeed, it may not be wise to try to fake sincerity. In a connected world, you cannot fool all the people all the time.
Geoff Mulgan is director of the think tank Demos.