Did they really say that?
It was Abraham Lincoln's 208th birthday last weekend. The US Republican Party's social media feeds honoured the 16th president by sharing a picture of his iconic memorial in Washington DC, with an inspiring quote laid over the top.
"In the end, it's not the years in your life that counts, it's the life in your years," was the message on Twitter and Instagram, also shared by President Trump.
There was just one problem: the words have been attributed to Lincoln many times over the years, but there is no evidence he ever said them. The post has since been deleted.
It was the latest example of a growing modern phenomenon, the fake political quote.
Some have said "fake news" could have swung the outcome of November's US presidential election. Bogus stories like "Pope Francis Shocks World, Endorses Donald Trump for President" were extensively shared online.
Made up quotes are perhaps more benign than fictitious news stories with a clear political agenda. But they still raise concerns, says James Ball of Buzzfeed News, who is writing a book about "post-truth" politics.
"If enough people share and believe these fake quotes, then they can contribute to the polarisation of politics, making each side think less of the other, especially as many partisans think fake news is a problem which affects primarily (or only) their opponents."
These fake quotes don't just come from right-wing politicians and activists.
In the days after the US election, a quote supposedly taken from a 1998 Donald Trump interview went viral online.
"If I were to run, I'd run as a Republican. They're the dumbest group of voters in the country. They believe anything on Fox News. I could lie and they'd still eat it up," the quote said.
It seemed too obnoxious to be true - and it was.
Fake George Orwell quotes are a specialty in left-wing social media circles. One example is "during times of universal deceit, telling the truth is a revolutionary act." There is no evidence the 1984 author ever said these words, but social media is awash with shareable pictures of them alongside Orwell's monochrome face.
So how do bogus quotes like this get into circulation?
"Sometimes people just want new followers or shares on social media, and either invent a quote or (naively or otherwise) lift a questionable one," says James Ball. "Others invent quotes as a hoax or parody to show up people they disagree with, or to fire up their own side - or simply to make money from adverts on fake news sites."
The internet means fake quotes can spread very quickly.
"It's easier to fabricate things than it is to debunk them," says Rasmus Nielsen, director of research at the Reuters Institute for the Study of Journalism at the University of Oxford. "As communication gets easier, there is going to be more and more of this stuff floating about online."
Can they be stopped?
Jenni Sargent runs First Draft News, which is working with social media companies and news organisations to look at innovative solutions to the problem.
"People are experimenting with the most engaging way to spread false information," she says. She wants news websites to come up with entertaining ways of debunking fake facts and quotes.
A blue tick next to a name on Twitter tells you the account has been verified as "authentic". Sargent wants to come up with ways to highlight unreliable sources, "like the opposite of a blue tick".
Facebook is introducing tools for German users to flag false stories ahead of that country's parliamentary elections in the autumn. Third-party fact checkers would mark unreliable stories as "disputed".
The BBC has also said it will fact check deliberately misleading stories "masquerading as news".
British MP Damian Collins is chairing a parliamentary inquiry into these issues, which will look at the possibility of news websites having "verified" markers. Collins thinks fake quotes attributed to electoral candidates could end up "distorting the democratic process".
How can we check?
Often verifying quotes is simply a case of rigorously searching through publicly available information, says Kim LaCapria, who works for rumour-busting website Snopes.
The volume of dubious content online is greater than ever before, but verification can be easier because far more information is digitised, she says. "It's actually pretty easy for average social media users to fact check online."
Her job involves looking at outright fake quotes, but also real quotes presented in a misleading way. For example, Al Gore has been ridiculed for claiming he "invented the internet". The former vice president did once say "I took the initiative in creating the Internet," but taken in full context, that line seems rather more modest.
We are less likely to expend energy verifying a quote which confirms our political beliefs, says LaCapria, an effect which psychologists call confirmation bias.
Whether a fake quote comes from the left or the right, it tends to have one common feature, she says. "It validates our preconceived beliefs or feelings, and that's often proffered as a valid reason to spread it."