Arturo Ramos had already had a cocktail or two when he signed away his rights 15 years ago.

The pictures, of him and his friend Javier in tuxedos against a rainbow flag at the LGBT pride parade in Washington, D.C., were taken by an acquaintance who was also an aspiring photographer. Ramos and Javier, who were not in a relationship, had been asked to be the two grooms atop a parade float decorated like a wedding cake. “It started out as this completely innocuous thing,’’ recalled Ramos, now a 44-year-old business professional living in Boston. “Who doesn’t like to have their picture taken?

The photographer snapped more than 20 pictures. After the parade and more cocktails, he approached Ramos carrying a consent form, a standard waiver just in case the images were ever sold. “Javier said, ‘This sounds kind of serious. Maybe we shouldn’t sign in this state.’ I was like, ‘What are the chances he’s ever going to sell the portfolio, and what are the chances someone is going to use it? Just sign it! What harm could come from it?’ ’’

The first e-mails and calls started barely a year later in 2003, when a Massachusetts court ruling opened the door to same-sex marriage. The photos had been sold to photography company Getty Images. Suddenly, photos of Ramos and his friend accompanied articles in alt-weeklies about same-sex marriage, a Latino health awareness campaign in Los Angeles, and an ad in a weekly paper for the San Diego Opera. Friends and family who saw the two men smiling from a billboard or topping an article about marriage mostly wanted to know when he’d gotten married — he hadn’t — and to offer their congratulations. Questions from his clients were a bit more awkward.

“But so far [the uses have] all been incredibly tasteful, so my premise — what harm could ever come from it? — has come true,’’ he said.

Ramos typically tells the story for laughs. But others have had more uncomfortable tales. In 2015, a judge agreed that Avril Nolan, an aspiring model living in Brooklyn, was entitled to defamation money from New York State’s Division of Human Rights after she became the face of the division’s ad campaign promoting the rights of HIV-positive New Yorkers. The campaign featured Nolan’s picture, sold by Getty Images, next to the words “I am Positive (+).’’ She is not. In a decision that stoked the ire of the HIV-positive community, a judge agreed that HIV is a “loathsome’’ disease from a defamatory perspective. She had also sought $450,000 from Getty, but settled the suit privately.

There are many other cautionary tales of people finding their own faces smiling or grimacing back at them from an advertisement or article. While there’s a certain element of “signer beware,’’ these stories also underscore the tacit understanding that the photo selling the product or the news story are not necessarily connected. That couple isn’t a couple; that HIV-positive woman isn’t. Humans put an inordinate amount of faith in what they see, so it is profoundly jarring to find out that their eyes have been lying to them. The deluge of stock photography in which we swim these days means that we’re being lied to more and more. And we rarely notice it.

In the age of fake news, this paradigm feels more than a bit sinister. Stock photos often accompany widely acknowledged fake news site articles. “We’ve seen that a lot of the fake news articles, unlike hoaxes and legends of the past, are photo heavy. They start by getting you with the impressive image and they construct a story that’s totally unrelated around it,’’ said Alexios Mantzarlis, director of Poynter’s International Fact-Checking Network. And any photos — stock or otherwise — lend articles more credibility.

Stock photography has existed since the 1890s. Photo libraries first served the editorial needs of the emergent magazine industry, offering staged photographs of people or animals. After World War I, news photo agencies sprang up to serve newspapers and wire services, and an increasing numbers of magazines such as LIFE. The business grew even larger in the 1970s, when stock photos began to flow into advertising and corporate marketing. By the 1990s, stock was a billion-dollar industry dominated by a few worldwide giants, including Getty and Corbis. Stock photos became, as Paul Frosh described them in his 2003 book, “The Image Factory,’’ “the wallpaper of consumer culture.’’

And then, of the digital world. In 2001 alone, Getty’s online sales exploded — from 48 percent of its total sales in the third quarter to 61 percent in the fourth. Meanwhile, the kinds of images that stock photo companies were selling were also changing. So was their clientele. As the amount of editorial content on the Web grew, so did the need to illustrate it somehow. While it would be possible to run an article in print without an image, it would be unthinkable to do so online. The stock image market is currently valued at around $4 billion, much of that in microstock — that is, low-price, royalty-free images. For mere “wallpaper,’’ there’s a lot of money and power involved.

“Images are very powerful in how they frame a story, whether or not they’re even related to the story,’’ explained Pamela Rutledge, a media psychologist at Fielding Graduate University. For example, a 2007 study found that pairing an image of a brain scan with an article about cognitive neuroscience research increases the reader’s rating of the scientific reasoning of the article. (Rutledge said that she was once told by a colleague to include images of brains in her talks to bolster her credibility.) “We know that the visual context of any story influences our understanding of it, it primes us to a certain way of thinking,’’ Rutledge said. “Whether you call it manipulation or facilitating information is entirely dependent on the intention of the producer.’’

Our interest in visual information is a part of what makes us human. “Images are a much more effective way to deliver information than text,’’ Rutledge said. “We are driven by a biological imperative for survival to get as much information as possible about our environment. It makes us feel safe.’’

Does visual information’s outsized influence on our perception and decision-making mean that stock photo companies have any special obligation to police the use of their products? Stock photography companies already do police their products’ use, sometimes aggressively so. Shutterstock, a company that earned nearly $500 million last year, stipulates in its licensing agreement that the buyer may not “[p]ortray any person depicted in Visual Content (a ‘Model’) in a way that a reasonable person would find offensive’’ or “[u]se any Visual Content in a pornographic, defamatory, or deceptive context, or in a manner that could be considered libelous, obscene, or illegal.’’ Image-tracing is getting easier, and stock companies do it, in part to make sure that people are paying for the images that they’re using (Getty is widely known for pursuing unauthorized usage of its images).

“Shutterstock proactively monitors some content and investigates every single claim of misuse we receive, many of which concern alleged misuse by Shutterstock customers,’’ said Heidi Garfield, general counsel for Shutterstock, via e-mail, noting that the company’s some 190,000 contributors are “empowered’’ to monitor their own images and raise concerns. “We periodically must seek the takedown of content . . . including, as recent examples, content that suggests an association with escort services, implies the intent to do serious harm to government leaders, or suggests that an individual suffers from a medical condition.’’

As for the much maligned fake news, Garfield pointed to the clause prohibiting buyers from using an image in “a defamatory or deceptive manner,’’ adding, “The proliferation of fake news, or websites that provide outlets for fake news, likely draws more attention to the misuse of visual content, and we are always responsive to claims of misuse.’’

But things get thorny in the place where questions of free speech are always thorny. Jim Pickerell, photographer and editor of stock photography trade news site Selling Stock, said via e-mail, “How would anyone in the stock photo business determine that the story a particular photo illustrates is fake or real?’’ Any photo can misrepresent; the question is intent.

Even so, stock photography is deceptive in a particular way: Ostensibly, the camera doesn’t lie, but our brains inevitably jump to conclusions about what it captures. Of course those two men in front of a rainbow flag are a couple! At times, stock photography erodes real, literal truth. “Stock photos do get used for the daftest things, and, in so doing, we’ve sort of accepted this suspension of disbelief when it comes to images,’’ said Mantzarlis. “And that’s dangerous, because seeing is believing.’’

There might be a role for stock photo companies in ferreting out fake news and blatantly dishonest reporting. “It’s a big-tent effort that’s going to be required, and there’s definitely space for action from these agencies,’’ Mantzarlis suggested. “It is in no one’s interest to have a Babelic Internet where it’s impossible to discern truth from untruth.’’ More practically, it might be valuable for stock photo companies to make sure their products aren’t being used inappropriately or just stolen. “You can’t yet get sued for publishing fake news,’’ he noted. “But you can get sued for stealing someone’s photo.’’

Shutterstock, for one, is willing to play, although it has a healthy wariness of determining what’s fake news in an increasingly hazy landscape. “It is likely that Shutterstock’s enforcement of its licenses can address some fake news, if, for example, such use is defamatory or deceptive,’’ said Garfield. “However, we have to be careful not to put ourselves in a position of taking a side on an issue that in some ways represents a proxy for other broader societal differences.’’

So who really has a responsibility here? No matter how divided they were on whether stock photography companies had any obligation to deal with fake news, nearly everyone interviewed for this story agreed that the audience does. If consumers become more adept at recognizing truth from fiction, then stock photography can go back to being harmless “wallpaper.’’

Until then, a little less trust in the images we see may be just what we need.

Linda Rodriguez McRobbie is an American freelance writer living in London.