Most of us have done it – ticked something off the To Do list when you haven’t exactly completed it. And so Steve Bannon, Donald Trump’s strategist, appears to have considered it a job done on hiring “5,000 more border patrol agents” (well, the money has been requested) and “suspend immigration from terror-prone regions” (blocked in federal court) as a photograph of his whiteboard list this week revealed.

The mythical whiteboards of Bannon’s office have been written about before, but never publicly seen. In a recent piece to mark Trump’s first 100 days in office, CNN described how “giant whiteboards” had been arranged in Bannon’s West Wing office, “lined up in four columns beneath the campaign theme: Make. America. Great. Again.” Floor-to-ceiling bookshelves and a sofa had been removed to make way for them, because who needs to sit and read and reflect when you’ve got policies such as “suspend Syrian refugee program” and “repeal and replace Obamacare” to be getting on with?

Now we know what sort of things the whiteboards contain. One of them provided the backdrop in a selfie, posted on Twitter, by minor reality star and “celebrity” rabbi Shmuley Boteach. They provide an illuminating, if not surprising, list of things Trump is planning to perpetrate on his country: cancel federal funding for sanctuary cities (an initiative that offers some protection to illegal immigrants and their families who fear deportation under federal laws); cut corporate tax rate from 35% to 15%; and build that wall (and “eventually make Mexico pay for it”).

Whiteboards, forgotten in the background, but easy to zoom in on in a photograph, can often be a liability. In April, a board in the background of an office at the Orlando Magic basketball team, taken and tweeted by a player’s agent, showed transfer-target players and revealed it was thinking about trading in one of its most popular forwards for a new player. In March, a photograph of two whiteboards by the side of the pitch at an England rugby union training day appeared to show the starting line-up for an upcoming match against Scotland. It was more or less accurate.

Facebook Twitter Pinterest Counterterrorism chief Bob Quick arriving at Downing Street and showing confidential papers to the press in 2009, which cost him his job. Photograph: Pictures/REX/Shutterstock

During last year’s Labour leadership election, Owen Smith was photographed with a whiteboard clearly showing login details and passwords for his campaign phone bank. It was posted on Twitter. More intriguing was the list of instructions for the phone canvassers, including headings that appear to read “Strong Owen” and “Weak Owen” (unfortunately Smith’s whiteboard handwriting is not as clear as Bannon’s). Weak Owenseems to have prevailed – Smith lost the election.

Usually it is documents, photographed by political paparazzi with long lenses, that provide the leak. In November, an aide to Conservative vice-chair Mark Field was photographed outside Downing Street carrying a memo that appeared to say the plan for Brexit negotiations was to “have cake and eat it”, adding that the “French are likely to be most difficult”.

The Downing Street photographer Steve Back took this shot, and is behind many more. He photographed a memo last September, held by a civil servant, that revealed the government’s plan for grammar schools; a year before, he photographed a document showing proposals to privatise Channel 4. In 2011, he snapped “protected” briefing papers held by then international development secretary Andrew Mitchell, which included notes on Afghanistan.

A picture Owen Smith posted on Twitter revealed login details and passwords relating to his campaign office. Photograph: Twitter

It is more remarkable when it happens to people who should be more careful. Kris Kobach, the Kansas secretary of state, met Trump in November when he was angling to become head of the US Department of Homeland Security – but a photo of the pair revealed that the document he was carrying included notes on tracking “high-risk aliens” and reducing the “intake of Syrian refugees to zero”. Kobach didn’t get the job. In the UK in 2009, a photograph of a confidential document – it was even marked “secret” – held by Bob Quick, Britain’s most senior counterterrorism officer, led to rushed terror raids and Quick’s resignation. In 2014, Hugh Powell, deputy national security adviser, was photographed carrying papers outside No 10 outlining that the government would not support sanctions against Russia over Ukraine “or close London’s financial centre to Russians”.

There are signs in Downing Street offices reminding people to cover their papers before they get outside, but it happens again and again. Did nobody learn anything from the “quiet batpeople”? In the BBC political comedy The Thick of It, Nicola Murray, the leader of the opposition, is humiliated after her version of “Mondeo man” or “Worcester woman” – the type of voter they need to win over – is revealed to be based on a bizarre idea about everyday superheroes called “quiet batpeople”. It was photographed on a handwritten memo carried by one of her aides. Of course, we later find out that the leak was deliberately orchestrated by scheming spin doctor Malcolm Tucker. When I spoke to Back about his track record in snapping “secret” documents, he said he was well aware that some people purposely leaked them. “It happened with Peter Mandelson one day,” he said. “He came out and deliberately showed his papers to me.”

It would be naive to think Bannon’s great whiteboard reveal is a gaffe. Boteach, who occasionally writes for the “alt-right” website Breitbart (of which Bannon is a founding member), wrote on Wednesday that Bannon sanctioned publication of the photograph: “We took a picture and he allowed me to tweet it.” The tweet, unlike many that were hastily taken down in embarrassment, is still there.