Accompanying an article on happily married husbands who end up falling in love with men, Woman’s World magazine ran a 1956 photograph of a happy-looking bride and groom. Running up the wedding picture was a ragged line meant to illustrate the destruction wrought by the husband’s jarring revelation. Friends and relatives of Michael and Agnes Grieco, the newlyweds in the picture, were shocked. So were the Griecos.

This was the first anyone had heard of Mr. Grieco’s secret life – Mr. Grieco included. Even more embarrassing for the Griecos – who were still happily married – was that they were known in their New Jersey community for counseling couples at their church.

It turned out that the photographer who had taken the couple’s wedding photos had submitted the pictures to a stock agency, which for a fee had licensed the picture of the Griecos to the magazine. Stock agencies save clients the trouble of arranging a photograph. But sometimes, using an old picture proves to be just asking for trouble.

When somebody who works for the mayoral candidate C. Virginia Fields illustrated a campaign flier by using a stock photo of Asians, it was clearly done to save the time and effort of organizing a photo-op and photographing the Manhattan borough president’s head bobbing in a multicultural sea. Reports that the Asian couple whose image was inserted electronically in a photo of Ms. Fields with other voters had never endorsed, or even met, the candidate set off a kerfuffle that hurt the candidate’s standing in the polls and led to the dismissal of her chief campaign adviser, Joseph Mercurio.

The $7 billion-a-year stock-photography industry has rules about how pre-existing pictures can be used. Anyone running an old picture, in a math textbook or a gardening supply catalogue or a newspaper, is expected to keep its original meaning intact. The exception is commercial pictures in which models have signed releases allowing their faces to be used to sell any product – so long as it can’t be seen as pornographic or defamatory.

With minimal industry wide ethical guidelines in place, however, great variances exist in how, or if, photographic agencies protect their images.

Some monitor every use, interviewing the client to ensure that the illustration is appropriate, while others reckon that paying clients can put pictures to any uses they fancy, so long as nobody is defamed.

What’s more, now that most agencies’ images have been digitized, copyrighted pictures can float around the Internet, at the ready for any wannabe pirates. A Stock Artists Alliance study this year used advanced software to determine that for every licensed image on the Internet, there are nine that have not been approved by the copyright holder. That opens the door to misuse and carelessness.

“Most people think of a photograph as the truth,” the name partner of a New York stock-photo agency, Woodfin Camp and Associates, said. “You didn’t expect to see a photograph and learn that someone’s been added or taken out. I wouldn’t say there are any written rules on my side, but it’s just not done.”

Most rules are implicit, and industry players are expected to act in good faith. It is generally agreed that combining, altering, or scanning photographs is a no-no, as is running a news photograph in a context that could be misconstrued – thus, it’s not kosher to illustrate an article on a steakhouse with a picture from a meeting of vegetarians.

An industry leader, Getty Images, allows cropping of editorial pictures, but not if it alters the picture’s meaning.

A photojournalist who recently founded World Pictures Network, Seamus Conlan, said the industry’s standards are spinning out of control, because sales representatives are eager to unload any old picture.

“We need to protect the integrity of the image and our sales team needs to know what they’re selling,” Mr. Conlan said. “If a photographer has a picture of an individual dying of heart disease in a hospital bed and a newspaper uses it with a story about people dying of AIDS, the family is going to be upset.”

Mr. Conlan cited two cases of stock photos’ getting into the wrong hands. One agency sold a photograph of a young Orthodox Jewish woman “sitting and doing her homework and being a good person” to a teen magazine searching for an illustration with a story about girls daydreaming about boys. In another case, a stock photograph of a high school principal vacationing at a Playboy hotel made its way into a magazine. His students saw the picture.