Washington Post readers saw a stunning photo, and an unusual caption, on the front page of Friday's newspaper.

The photo depicts a plane taking off from Reagan National Airport, the 14th Street Bridge in the foreground and the orange glow of the setting sun in the background. The photo references the Air Florida jet that crashed into the bridge 30 years ago.

This image ran on the front page of Friday's Post. (Bill O'Leary/The Washington Post)

The caption included a note: "This image is a composite created by taking several photos and combining them with computer software to transcend the visual limitations of standard photography."

That raised more questions for me than it answered, so Kenny Irby, Poynter's photojournalism faculty, and I called Michel du Cille, director of photography for the Post.

The answer involves not Photoshop but HDR (high dynamic range) photography, which combines images with multiple exposures into a single image.

The Nikon D4, for example, can take two images with different exposures and combine them into a single image. The photographer can then use software to combine up to nine of those images into one. You may have noticed an HDR setting on your new iPhone, too.

“The technology offers broader dynamic range in tone and detail, and does not change the authenticity of the scene or situation,” Irby told me. It's particularly useful when part of a scene is very dark or light, and choosing a single exposure means that only a portion of the image will be properly exposed.

That's why Post photographer Bill O'Leary chose HDR this time, du Cille said.

“I think Bill was looking for the effect that HDR gives at a tough time of day,” du Cille said. O'Leary used software to combine five images with different exposures.

Editors wanted to disclose that the photo was taken with an unconventional method. But copy editors thought that the average reader wouldn't know what HDR is. So they settled on the language in the caption, which said the image was a “composite.”

“We were trying to be upfront, to tell the reader we used technology to achieve this result,” du Cille said. “ 'Composite' is probably what confused people, because in this case, it is a composite of exposures, not of an element” of the photograph.

Irby said the Post had the right idea by disclosing the technique, but could've done more to explain how and why that photo was chosen. “The caption definitely does offer you new insight about the photo. However, it presents more questions than usable information.”

Du Cille said he may write something for the Post explaining how the photo was made and why it was used. But he said that the issue is transparency about techniques, not the technique itself.

“I want our photographers to be experimenting with a range of things, not just technologies,” he said. Although HDR is uncommon now, “Ten years from now, HDR may be built into cameras, and who will know it?”

But Sean Elliot, president of the National Press Photographers Association, said, "HDR is not appropriate for documentary photojournalism." The organization's code of ethics say photographers should respect the integrity of the digital moment, "and in that light an HDR photo is no different from any other digital manipulation."

"By using HDR," he told me by email, "The Washington Post has combined different moments, and thereby created an image that does not exist. The aircraft visible in the final product was not there for all the other moments combined into the final, and that alone simply raises too many questions about the factual validity of the actual published image."

HDR wasn't the only option for this situation. On the same night O'Leary took a similar photo without HDR; rather than aim into the setting sun, he took the image from the other side of the bridge and used the setting sun to light it.

This photo was taken without HDR. Du Cille said this image wasn't as powerful as the other one. (Bill O'Leary/The Washington Post)

NPPA's Elliot said that photo suggests that the HDR image wasn't necessary. "The selection of photos is by nature a subjective process and the alternate, unmanipulated, image looks to be as strong a documentary image of the bridge in question as one could want."

“I think the picture that we used is the better picture,” du Cille said, even though it required a more complicated – and perhaps confusing – caption. “It's more pleasing to the eye because of the sunlight on the water, the sunlight in the sky, the blueness of the sky, the clarity in the bridge.”

This is the second time in a month that the Post has used HDR photography on the front page; the other time was for the winter solstice. It will be a while before they try it again, du Cille said.

“It would become its own cliché.”

Kenny Irby contributed to this story.