The daguerreotype shows a 7-year old girl. Her face is pale, her expression somber. Her elegant plaid dress, trimmed in lace, and the notebook on the cloth-covered table behind her, suggest that she comes from a prosperous family.



Though modest, the photograph taken in Boston in 1855, is actually historic. It shows not a white child but a black girl — Mary Mildred Williams — who was born into slavery. It was an image so compelling to white Americans at the time that it helped transform the abolition movement. Housed in relative obscurity at the Massachusetts Historical Society, the daguerreotype was recently rediscovered by the photographer and scholar Jessie Morgan-Owens while researching her dissertation.

“Mary’s daguerreotype was one of the first images of photographic propaganda and one of the first portraits made solely to prove a political point,” Ms. Morgan-Owens wrote. “It marks a forgotten moment in media history: when photography, introduced to the United States in 1839, first began to make its tenacious claim on our sympathies and on our political points of view.”

Mary is now the subject of Ms. Morgan-Owens’s groundbreaking book, “Girl in Black and White: The Story of Mary Mildred Williams and the Abolition Movement” (W.W. Norton & Company). Mary and her family had been enslaved in Virginia. Her father, Henry Williams, escaped to Boston and worked with members of the Vigilance Committee, which provided legal and financial help for fugitive slaves, to free his family in the South. Senator Charles Sumner of Massachusetts, a prominent ally, saw an opportunity in the family’s story.

After helping to secure her freedom, Mr. Sumner enlisted Mary — whose light skin reflected the legacy of generations of sexual violence against enslaved women — as a poster child for the movement. He saw in her experience a parallel with Mary Hayden Green Pike’s popular abolitionist novel, “Ida May: A Story of Things Actual and Possible,” in which a white girl is kidnapped, her skin dyed brown, and sold into slavery. Ms. Pike’s fictional portrayal presumably motivated white northerners to turn against slavery and the Fugitive Slave Act, which required that runaway slaves be returned to their masters, by stoking the fear that even their children could be vulnerable.

By highlighting the light-skinned Mary, Mr. Sumner appealed to the prejudices of white Americans who were potentially sympathetic to the abolitionist cause. Employing her image to suggest that slavery was not bound by skin color, he transformed it into a benign icon: a symbol of an institution so malevolent that even innocent children who were practically white were swept up in it; a rallying cry against slavery through the lens of white self-interest and an excuse to feel virtuous without committing to absolute racial equality.

Mary Mildred Williams’s fame was fleeting. For many years, she worked as a clerk in the registry of deeds in Boston, and died in New York in 1921.

“To use a 21st century metaphor, I believe stories like Mary’s offer a patch in the virulent social programming about white girlhood that American society has inherited from that time,” Ms. Morgan-Owens said. “She complicates the visual language of antislavery. Meanwhile, the ignorance and nearsightedness that occasioned this story can still be found in activist communities today, as evidenced in narratives of pity, savior complexes, and colorism, in who gets chosen to be a poster child.”