News media have been prevented from showing a photo of David Cameron with fellow Oxford dining club members.
The image of the Tory leader, which shows him in about 1986 dressed in the uniform of the elite Bullingdon Club, has appeared in several newspapers.
It is thought Labour was planning to use the picture on an election poster.
But the photographers who have withdrawn it say they acted for commercial reasons and have had no contact with the Conservative Party.
The Conservatives have also denied asking the Oxford-based company Gillman and Soame, who own the copyright, to withhold permission to show the picture.
The photographers told BBC Two's Newsnight they had taken a "policy decision," after the picture appeared in national newspapers, not to allow any school photographs they own to be published.
BBC Two's Newsnight has commissioned a painting of the scene shown in the Bullingdon picture.
The Bullingdon Club is famed for its hard drinking and bad behaviour, and Mr Cameron has always refused to talk about it.
The club's members have become notorious over the years for vandalising restaurants and trashing students' rooms.
Former members include Alan Clark, who gained fame as a political diarist after serving as a junior minister in Margaret Thatcher's government.
Andrew Gimson, author of The Rise of Boris Johnson, said: "I don't think an evening would have ended without a restaurant being trashed and being paid for in full, very often in cash.
"A night in the cells would be regarded as being par for a Buller man and so would debagging anyone who really attracted the irritation of the Buller men."
In the photo Mr Cameron and several other Bullingdon members, including the young Boris Johnson, now shadow higher education minister, pose in their £1,000 uniforms of blue ties, tails and biscuit-coloured waistcoats.
The Labour Party is thought to have been planning to use the image to attack Mr Cameron at the next general election.
Commentators, including former Labour deputy leader Roy Hattersley, have said it is potentially far more embarrassing to the Tory leader than the recent story about him taking cannabis at Eton.
Newspaper columnist Peter Hitchens told Newsnight: "I think it tells us something about David Cameron that he doesn't much want us to know, that he is not the ordinary bloke that he claims to be.
"That he is actually much grander and much more aristocratic than he has made out."
But Tony Blair also has an embarrassing photo from his student days.
The photo of the prime minister from the 1970s shows him with fellow members of an Oxford university dining club.
It has been published many times before in a cropped format - but Newsnight has shown that the full photo shows him making what appears to be a rude gesture.