“It is the visual stories that have staying power,” a picture editor once wrote. From time to time an image condenses a public issue into human form so powerfully that it becomes both messenger and symbol. The latest is last week’s photograph of the bodies of Óscar Alberto Martínez Ramírez and his 23-month-old daughter, Angie Valeria, floating face-down near the bank of the Rio Grande, on the US-Mexico border.

The child’s arm, draped across her father’s neck, emerges from inside his shirt, where presumably he had tried to secure her. It gives the image a potent poignancy. “The tenderness, the way he never let her go. You can see the way he protected her,” said Rosa Ramírez, his mother in El Salvador, from where Martínez, his wife, Tania Vanessa Ávalos, and their daughter had begun their attempt to reach the US.

Sometimes journalism legitimately confronts society with the consequences of what it perhaps prefers to deny or forget

In death, father and daughter join a small band of people whose personal disasters, photographed, tell a larger truth. Published, the images spread that truth. Alan Kurdi, lifeless aged three in the arms of a policeman on the Turkish beach where his body washed ashore, is Europe’s migrant crisis of 2015-16; Omran Daqneesh, five, staring through a paste of dust and his blood, is the conflict in Syria; Phan Thi Kim Phuc, the running naked, burned “napalm girl”, is the Vietnam war.

To weigh images such as these, the standards guiding most serious newsrooms include: do not use gratuitously; provide context; give appropriate warnings; consider the sensitivities of the grieving; and respect the dignity of the deceased. And explain your decision – even readers who would have made a different call, who may be angered or upset by the image, will appreciate an account of your reasoning.

When the Guardian published the image on digital platforms and in print, dozens of readers disagreed strongly. Some thought it disrespectful, others insensitive, even racist. Anguished emails flowed in. Several readers who endorsed the journalistic imperative nevertheless protested at the way the Guardian handled the image.

The editor-in-chief, Katharine Viner, told me: “We thought very hard about whether to use the photograph. We decided that it is an incredibly powerful image that would have a great impact and perhaps make people understand the human cost of the migrant crisis in the US. I was struck that one of the Democrat candidates for president said of the picture, ‘Trump is responsible for these deaths.’ Our job is to report the news, however shocking, and part of that will sometimes include showing distressing images. We also try to run contextualising material alongside such pictures – here we used a powerful news report as well as a first-person piece from the photographer explaining why she had taken the picture. We used the image very powerfully on the front page of all our sites and on the front page of the next day’s newspaper as well. It was a very distressing photograph and I understand very well why some readers might question our decision to use it. However I believe that it was such an important image, about an important story, that it needed to be seen.”

Initially published online with a warning of “graphic images” that gave readers a chance to decide whether to view it, the picture later spent several hours near the top of the front page of the website, where every reader unavoidably saw it when they arrived, including some who told me they had earlier chosen to avoid it.

When readers clicked through to the main news story and the photographer’s contextualising account, the warning was useless because it appeared with, and under, the image. Thumbnails of the photo appeared in the site’s “most read” and “related stories” lists, draining it of power and solemnity, and making it seem merely facilitative, a cosmetic add-on. (Efforts were made to reduce this effect.) At one stage, an automated advertisement with a “wet socks” theme accompanied the coverage (and was swiftly removed when a reader flagged it). Encountered via the Guardian’s Facebook presence, the image initially lacked warning or context. Some reported a similar experience with the Guardian app.

Late in the day, the coverage on the website front was back to the headline with a warning, so readers could choose whether to click and look. On 27 June the newspaper’s front page carried the image prominently, rather than, say, a pointer to it on a page inside.

I support the decision to use the image. Sometimes journalism legitimately confronts society with the consequences of what it perhaps prefers to deny or forget. Shock is sure, effectiveness less so.

And I sympathise with the challenges editors face in managing their content on different platforms, some third-party-controlled. But valid criticisms were made by readers of how the Guardian handled this image, and lessons can be learned before the inevitable next time. Ineffective warnings, in particular, risk being perceived, however unfairly, as cynicism, and that corrodes trust.

• Paul Chadwick is the Guardian’s readers’ editor