David Cameron in front of the poster at Monday's launch
David Cameron has said he "certainly hopes" a picture of him on a Tory campaign poster was not airbrushed.
The Tory leader appeared in front of the giant poster image as he launched the pre-election campaign on Monday.
Since then there has been speculation in newspapers that the picture had been "touched up" or "airbrushed".
Asked by the BBC if that was what had happened, Mr Cameron said, "I certainly hope not," before adding, "I did not produce the picture or the poster."
He said he was responsible for the words on the poster, which was a pledge to cut the budget deficit but not the National Health Service.
"I made the decision that I wanted a strong positive start to the campaign and a strong positive poster," he told BBC Radio 4's Today programme.
He also repeated his call for Mr Brown to call an immediate general election, following Wednesday's bid by two former cabinet ministers to trigger a secret ballot on the prime minister's leadership.
He told the BBC: "You just have to ask yourself: 'How much time do you think senior ministers spent yesterday thinking about the budget deficit, about the education of our children, about the war in Afghanistan, and how much were they thinking about their own careers?' for you to realise that, as we've put it pretty clearly, we cannot go on like this.
"We've got to have an election and a change of government."
A general election must be called by early June but 6 May is widely thought to be the most likely date.