By TIM STELLOH via The New York Times

PORTLAND, ORE. — On a cold, rainy morning in January of last year, Matthew Medlin hopped a refrigerated freight car in downtown Portland, Ore., and headed north. Mr. Medlin is 33 and homeless, with dagger-like stripes tattooed above his eyes and four dots below them — symbols of what he described as his belief in lycanthropy, the mythical transformation of humans into wolves. He has been a habitual methamphetamine user for years. He’s schizophrenic.

In Mr. Medlin’s telling, when he arrived at the Portland Terminal railroad yard, he felt something there — a person in danger. What followed, however, was not a rescue effort, but a five-hour standoff with police in which Mr. Medlin was said to plead with officers to shoot him.

Later, in an interview from jail, Mr. Medlin denied much of what the police said about their confrontation, though he agreed with this detail: It ended when an officer scaled a scrap car and tasered him. His arrest no doubt would have made local news.

But the story quickly spread across national and international media for one reason: the mug shots he’d collected over the years. As The Sun newspaper in Britain put it in a headline: “Shocking mug shots reveal how methamphetamine and a life of crime ruined young man’s model good looks.”

Mr. Medlin, like Jeremy Meeks (the “hot felon,” of viral booking photo fame), was famous, for a moment, because of his mug shot. Other mug shots go viral, too; the faces of the already famous at a low moment. Tiger Woods’s image joined that lineup after he was arrested last month.

We can guess at why we want to see the photos of the famous facing legal trouble, or rubberneck at Mr. Medlin’s transformation — as powerful an antidrug yarn as Nancy Reagan could ever have spun.

Why, though, did we see the images in the first place?

The simple answer is as routine as the booking photo itself: They’re public documents.

There’s a more complicated answer, too, since the United States professes a belief in blind justice while eagerly distributing photos of its accused. It’s not that police departments in England and Canada don’t collect photographs of people they’ve arrested; they just release them only on occasion, such as when there’s a jailbreak or a murder suspect on the loose. As Eddie Townsend, spokesman for the City of London Police, put it: “It goes back to the principle of innocent until proven guilty.”

The cultural idiosyncrasy in the United States can be traced back more than a century, to when the photograph was among law enforcement’s most sophisticated criminal identification tools. But over the decades, the booking photo evolved into something quite different.

Most states don’t limit their distribution, and some police departments believe putting out these images is an important part of transparency and serving their communities. Sheriff’s offices in large and tiny counties alike now post mug shots to slick, constantly updated websites. Under its former sheriff Joe Arpaio, Maricopa County, Ariz., even held a contest in which visitors voted on a mug shot of the day.

Local TV affiliates present them in slide shows, and crime-fighting social media groups use them to identify people connected to local crimes. The Smoking Gun website assembles them into all manner of categories, including “cleavage,” “fogeys” and “B-List.”

Privately run online databases like arrests.org let readers tag and comment on them, while Jailbase shuffles them through a smartphone app. Some sites have been described as extortion operations, posting booking photographs online, then charging exorbitant removal fees.

Free expungement clinics help the more desperate scrub their criminal records, while companies like EraseMugshots.com offer “removal” services for a fee. Lawmakers in more than a dozen states have tried reeling in the more pernicious practices of some mug shot entrepreneurs, according to the National Conference of State Legislatures.

Why are people so obsessed with these photos? A Rutgers sociologist, Sarah Esther Lageson, who has been studying the explosion of digital mug shots for nearly a decade, said they offer a view not just into the darker recesses of someone’s life but also into an essential government process that many of us never see or experience.

Professor Lageson interviewed 27 people at Minnesota expungement clinics over two years beginning in 2014 and found that people whose mug shots were easily available online had been fired and rejected from jobs — or afraid to even apply in the first place. One woman had been unable to find decent housing; another was kicked out of her church.

Most of the people Professor Lageson interviewed didn’t bother contacting the sites that were publishing their images. Some thought it wouldn’t do any good, given the official-sounding language some sites used. Consider Mugshots.com, which describes itself as a “search engine for Official Law Enforcement Records” — a mission it says is protected by an assortment of federal and state laws and two constitutional amendments.

Not everyone has been chastened by this legalistic language, though. In Illinois, three men seeking class-action status filed a suit last year describing the site as an extortion racket that, among other things, routinely published out-of-date or inaccurate information for a single purpose: to drive people to a prominently advertised “sister” site — unpublisharrest.com — which charged from $399 (to remove a single arrest) to $1,799 (for five).

A lawyer representing Mugshots.com, David Ferrucci, denied this. He said that the site is as much a crime blog as anything else. He pointed to its aggregated posts about accused sexual predators and murderers, and compared it to The Chicago Tribune’s “Mugs in the news.”

Besides, Mr. Ferrucci added, shouldn’t the focus be on the draconian elements of our justice system? “Instead of shooting the messenger, the purveyor of the public records, maybe we should lessen the impact of the prison industrial complex,” he said. “That’s really the tragedy here — how easy it is to get arrested.”

Sites like Mugshots.com aren’t the only ones fighting for continued, broad access to booking photos. In 2013, The Detroit Free Press sued the Justice Department after it refused to release mug shots of four police officers accused of corruption. Federal authorities have considered the release of a booking photograph an invasion of privacy, and in its ruling last year, the Sixth Circuit Court of Appeals agreed, overruling a 1996 decision that allowed the release.

The Free Press appealed this decision to the United States Supreme Court; last month, the court declined to hear the case.

Still, dozens of news organizations and press advocacy groups backed the newspaper up in court, including the Reporters Committee for Freedom of the Press. A lawyer there, Adam Marshall, described the mug shot as a memorialization of one of the most important processes of the criminal justice system — the arrest. What if the police arrested the wrong person? What if the officer assaulted that person? “The public expects information from the government about what they’re doing,” Mr. Marshall said. “The photo provides the public with that information in a way that a name doesn’t.”

Back in Portland, inside the drab interview room of Multnomah County’s sleek, downtown jail, Matthew Medlin wasn’t sure what to think about how his mug shots had turned him into a grim type of celebrity. He viewed the images, in part, in those terms — “It’s kind of cool that I’m being glorified a little bit,” he said — though he hoped their impact didn’t stop there. “If there’s a reason or a chance that this can actually benefit me, or people like me,” he said, then “maybe somewhere down the road it’ll help us get the help that we need.”

He seemed hopeful. He had been moved from a jail cell to Oregon’s main psychiatric hospital in the state capital, where he was signing up for classes on how to deal with mental illness and how to defend himself in court. “It’s just a good rehabilitation vibe,” he said. “It’s well needed, I think.”

Tim Stelloh is a freelance journalist. This article was produced in collaboration with The Marshall Project, a nonprofit news organization focused on criminal justice.

Photo illustration based on mug shots of Matthew Medlin. Credit Alex Tatusian/The Marshall Project