It has a lot to do with this website, MyDavidCameron (click on it -- it's excellent), which has collated some of the best efforts at remodelling the Tory leader's 15-foot election poster, and provides a template that allows you to have your wicked way with it.
Childish? Perhaps. Funny? Definitely. Even Labour HQ has got in on the action, inspired by the viral success of this website and the plethora of sarcastic slogans sitting next to Cameron's eerily smooth face. (Here's a cracker: "I love the BBC so much, I want to cut it up into little pieces and give it to all my friends.")
In what is probably a slightly less controversial line of attack than the whole Eton thing, Gordon Brown went hard on the airbrushing today at PMQs. Some highlights:
"If you can't get your photo right, it's pretty difficult to get your policies right."
"He's getting even much redder than he is on his poster. What you see clearly is not what you get."
"His airbrushed poster had better lines on it than the lines he's giving today."
Labour's home page now features the party's very own version of the poster (see above). Possibly not as funny as the Elvis version (but then, I have a puerile sense of humour). Yet there's a serious point to be made here. James Kirkup, blogging at the Telegraph about Brown's comments, asks whether "Labour's strategists have decided that Mr Cameron's I-am-the-message campaign is vulnerable".
The presidential-style poster was, presumably, a response to the fact that the Cameron brand consistently leads over the Conservative one. The obvious airbrushing provides, for the opposition, a useful political metaphor for dissembling, concealing the truth. It will be interesting to see whether this line of attack has any real impact on voters.