NEW YORK — The woman in Dorothea Lange’s most famous photograph, often labeled simply “Migrant Mother,” is, among other things, rather beautiful. Her face may be weathered and lined with care, but it also suggests sensitivity and intelligence. She is tired but handsome, rather like the man in the 1940 photograph “Migratory Cotton Picker,” which opens the exhibition “Dorothea Lange: Words & Pictures” at the Museum of Modern Art.

Their beauty isn’t often remarked on. Rather, these photographs are bound up with words, with their captions and with a larger cultural conversation about poverty and despair in America during the Depression and after. “Migrant Mother” was made in 1936 but wasn’t known by that title until 1952, and the woman in the image, Florence Owens Thompson, remained anonymous to the larger public until 1978. She is an icon of American suffering and perseverance, and she is also Cherokee, another word not appended to the image until decades after it was taken.

It may seem obvious, even uninteresting, to mount an exhibition about how words are attached to photographs. This happens all the time, so often that we don’t think about it. In newspapers, every image is captioned. When we read biographies or history, we reflexively turn to the photographs in the middle of the book to attach images to the words we have absorbed. We are fast approaching the two-century mark in the history of photographs, and we have never been more suspicious and verbal in our relationship to them: What does this image show? Where was it made? Can I trust it?

But that hasn’t always been the case. Throughout the history of photography, especially among photographers who began making photographs as art, there has been a contrary argument about words and images: A good photograph shouldn’t need explaining. If photography is art, and art is self-sufficient, then photographs should stand alone and convey their meaning through the image, not its description.

Lange made some of the most compelling images of the past century, but she had no problem with words, and would have been impatient with any discourse that abstracted photography from the larger world. “All photographs — not only those that are so called ‘documentary’ . . . can be fortified by words,” she said. It’s a curious choice of words. “Fortified” means strengthened, in particular against any effort to assault or dismantle the image. Lange’s images were often confrontational — calls to conscience and part of a lifelong interest in social justice, fairness and decency — so they needed to be fortified against indifference or cynicism.

Many of her photographs also appeared surrounded by words, in such popular magazines as Life and Look, and in books known as phototexts, with accompanying poems or poetically evocative statements culled from conversations with the people depicted. Lange also took extensive field notes while photographing, and, working in the 1930s with her husband, the economist Paul Schuster Taylor, she contributed images to extensive government reports documenting social conditions during the Depression.

Her images also inspired words from others, including John Steinbeck. In 1938, poet Archibald MacLeish used “Migrant Mother” in a phototext called “Land of the Free,” where it appears opposite a line from a poem he wrote to “illustrate” images made by photographers working for the Farm Security Administration and other government agencies: “Now we don’t know,” which was an enigmatic way of suggesting a creeping anxiety that had infected the American Dream. The same image also appeared in Nazi propaganda in 1943, with a mocking reference to President Franklin D. Roosevelt’s New Deal.

The range of ways that single image has been used and abused helps one understand why many photographers are wary of using words to define images. But limiting oneself to the image alone doesn’t fix its truth any more than a good or bad caption. When “Migrant Mother” was reproduced in a bulletin for MoMA’s first photography exhibition in 1940, it was printed much lighter than other versions, so that the woman appears not just white, but pale, her arms almost bleached out, and the hair of the two children who hide their faces behind her is almost blond. It feels like a racial erasure, with any hope of seeing her as Native American effectively whitewashed.

More fundamentally, thinking about photographs without words is essentially impossible, and ignoring the larger, word-based context of their appearance limits their richness. When Lange’s photographs of Mormon communities appeared in Life magazine in 1954, the article began opposite an advertisement for a consumer object unlikely to be found in traditional Mormon communities — a GE coffee maker — with the company’s tagline, “Progress is our most important product,” creating an ironic contrast to the isolation and insularity seen in Lange’s images.

The beauty of many of Lange’s subjects, including Florence Owens Thompson, isn’t accidental. Lange began her career as a portrait photographer, and she had an intuitive sense of what makes a face compelling. But the beauty also creates a spark, a desire to know more and interrogate the image. Like the woman in “Migrant Mother,” the man in the 1940 “Cotton Picker” has a face that seems young and old at the same time, a contradiction that starts the mind working, keeping it engaged with the image. It may be a primitive appeal to emotion — why is this beautiful person in such an ugly place? — but it is a powerful invitation to want to know more, to reach out, to demand a better world.

And beauty, for Lange, was fundamental to photography. For as much as she embraced words for their fortifying power, she was compulsive about finding images that spoke sharply, clearly and with purely visual power. In one of the exhibition’s most haunting photographs, “Tractored Out, Childress County, Texas,” a lone house, not much more than a cabin, sits forlorn and abandoned in a field whose machine-made furrows have consumed any yard or grass or other signs of humanity that might have once graced it. It is a devastating image of the Dust Bowl, but also a perfectly, beautifully made image.

In a documentary film included in the exhibition, showing Lange late in life as she prepared for a major retrospective, the camera captures “Tractored Out” as Lange says: “I’m just really beginning to sense what’s in this medium.” The ambivalence and modesty in that statement, made by one of the great photographers of the age, is touching. But it also suggests her genuine uncertainty about the tension between an abstract, formal beauty and the larger social context of photography.

Lange once said, “The camera is an instrument that teaches people how to see without a camera,” which is probably the best way to understand how she understood the dynamic between art and documentary value in her work. She could make images that are as perfect and self-contained as anything by Edward Weston or Walker Evans. But the image always pointed beyond the image. The camera could help one see both beauty and ugliness in the world, refining our sense of both social and artistic vision.

There were plenty of photographers who feared that words might take you outside of the image, and it is a reasonable fear. Lange understood that was exactly the point. A good photograph must deposit you in the world.

Dorothea Lange: Words & Pictures Through May 9 at the Museum of Modern Art, New York.