Image copyright AP Image caption Margaret Thatcher is credited by many as a British pioneer of political photo ops

Pictures of politicians feeding orphaned lambs, pulling pints and bowling can only mean one thing - an election is on its way. But how did the cliché of the political photo call begin? And is there still a point to it all?

Since the start of the election period, pictures have emerged from the campaign trail every day.

Nick Clegg has met a poorly hedgehog, painted a wall, been bowling and bounced along treetop walkways. David Cameron has been to the Game of Thrones set.

Ed Miliband has been snapped picking up fish and chips and has posed in countless selfies. Nigel Farage has been learning how to make hinges.

And with more than a week to go until voters hit the polling stations, the political posing is not over yet.

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The ritual of the political photo opportunity is nothing new - the precedent for such a thing was set by the Iron Lady almost 40 years ago.

Image copyright Getty / PA Image caption The Iron Lady's photo calls included shots of her holding a calf and meeting a chimpanzee

In 1979, before she became prime minister, Margaret Thatcher visited a field in East Anglia where she met Maggie the calf.

Mick Temple, professor of journalism and politics at Staffordshire University, said that particular photo call was widely considered to be the first profile-building event of its kind.

"She was there for no other reason than to be photographed, demonstrating to countryside voters they could trust her," he said.

Image copyright PA Image caption John Major became known for his soap box moments

"Since then, photo calls like that have dominated the media."

Mrs Thatcher's political campaigning continued to be documented with pictures of her visiting factories, meeting a chimpanzee and touring the Coronation Street set.

And other politicians followed suit.

Her successor as prime minister, John Major, developed his own technique when it came to getting his picture in the papers.

In 1992, a couple of weeks before a general election, Mr Major climbed onto his soapbox and urged voters in Cheltenham to elect John Taylor as the first black Conservative MP.

Mr Taylor did not win, but Mr Major's style of soapbox campaigning, which he used on numerous occasions, was considered by some to be a reason for his party's election victory that year.

A decade on, and Labour prime minister Tony Blair became a dab hand at the art of the photo call.

Image copyright PA Image caption Some photo calls where politicians tried to act cool have gone down better than others

In 2003 he enjoyed an "impromptu jamming session" with David Blunkett and a group of pupils from a community college in Sheffield.

"Mr Blair picked up lead guitar, while his home secretary kept a steady beat on the drums as both men joined in a 12 bar blues piece with school band The Jabberwocker," the BBC reported at the time.

But photo calls do not always have the desired effect. When William Hague became leader of the Conservative Party in 1997, he participated in a photo shoot on a theme park log flume.

The apparent attempt at projecting a more youthful image, wearing a baseball cap, was deemed by many to be a fashion faux-pas,

Image copyright PA / Getty Image caption Liberal Democrat leader Nick Clegg has been pictured bowling, meeting a fish, and treetop walking

Picture not-so-perfect

Neil Kinnock's walk along the beach in Brighton after his election as leader of the Labour Party in 1983 was remembered for the wrong reasons when he took a tumble on the sand

Gordon Brown's 2009 visit to a south London school went somewhat awry when photographs featured his smiling face against a backdrop of a swastika - part of a school project about life under the Nazis

During London 2012, Boris Johnson was famously left dangling above crowds at Victoria Park when a zip wire he was trying out lost momentum

The infamous Ed Miliband bacon sandwich shot, taken last year in Covent Garden market, showed the Labour leader sinking his teeth into the snack with apparent difficulty

And most recently, a photo op at a school went slightly wrong for David Cameron when he was reading to six-year-old Lucy Howarth, who was pictured with her head on the desk

Although Mrs Thatcher set the precedent for photo calls, her style of unplanned, off-the-cuff shots are long gone, according to one long-serving photographer.

Stefan Rousseau, the Press Association's chief political photographer, said the run-up to this election had involved "more control than I've ever seen" with regard to snaps of politicians.

"Things are well controlled and organised, thought about for days or weeks beforehand. I can't think of the last time something happened spontaneously," he said.

One set of planned pictures was taken on Easter Sunday when David Cameron took a "break from campaigning" - his words on Twitter - and went to an Oxfordshire farm to bottle-feed an orphaned lamb.

Image copyright Reuters Image caption David Cameron touching noses with an orphaned lamb was planned

Image copyright PA Image caption While his tender moment with newborn daughter Florence was not orchestrated

Political commentators have suggested the it was intended to showcase Mr Cameron's softer side - but Mr Rousseau said a more spontaneous photo he took some years before did a better job of that.

"I went to take pictures of David Cameron and his daughter Florence in Cornwall a few days after she was born. He came in the room and played with her for a good few minutes, he touched her nose, got close to her.

"After a few minutes, he asked, 'So what do you want me to do for the picture? And I said, 'I've got it'.

"His interaction with her was totally natural, and it made him look like a good father," Mr Rousseau said.

Image copyright PA Image caption UKIP leader Nigel Farage's uses photo ops in the pub and elsewhere to appeal to voters

Whether pre-planned or spontaneous, politicians and their campaign teams have an important aim in mind when it comes to photo calls - to make them look like "normal people" with whom the public can identify.

Professor Temple points to UKIP leader Nigel Farage's regular use of the "posing in a pub with a pint" technique as an example.

"The pictures identify him with his core constituency. He's putting himself across as the sort of bloke you'd want to stand and chat with.

"It's about creating a personality, telling your core constituency - 'look at me, I'm normal. Look at me, I care about the same things you do'."

Mr Cameron's "legendary" use of family holiday photo calls was "appealing to Middle England" and "connecting him with the electorate in a way that goes beyond how politicians are normally portrayed, sparring in parliament or being grilled by Paxman," Prof Temple added.

Image copyright AP Image caption Mr Cameron had a selfie with a worshipper in Kent during the Sikh festival of Vaisakhi

Image copyright AFP/Getty Image caption Mr Miliband posed for a selfie with a young supporter in Lincoln

One candidate who has not been pictured at an animal sanctuary or posing with pints as part of his election campaign is Ed Miliband.

Last year, the Labour leader said he was "not going to be able to compete" when it came to looking good in a photo opportunity.

"If you want the politician from central casting, it's just not me, it's the other guy," he said.

Mr Rousseau said Labour's aim during the campaign so far seemed to have been to make Mr Miliband "look prime ministerial" and use his speeches and question and answer sessions for photos instead of the time-honoured action snaps with animals or props.

Image copyright PA Image caption Conservative George Osborne learned how to make a pizza on the campaign trail

Image copyright Getty Images Image caption Green Party leader Natalie Bennett posed with a portrait of herself made by a Birmingham artist

Mr Rousseau said he would prefer to see more natural, unscripted photo shoots come back into favour.

"If you've got something which just happens on the spur of the moment, it comes through in the picture - you can see spontaneity.

"There's something real going on. When you do ones which have been set up, you take the pictures, look at them, and think 'that looks set up'.

"If we can see that, the public can as well."

Professor Temple is also not entirely convinced that the photo ops succeed in their aim of humanising politicians to voters.

"People aren't stupid. They can see through the pictures," he said. "They'll base their decision on other areas. The idea they're going to vote for someone who looks best feeding a lamb is risible.

"But, on the other hand, the more pictures you've got out there not presenting negative images of you, the better. Plus the media has an insatiable appetite for this stuff and almost infinite space to put it.

"In an election as close as this, anything could make a difference."