From Bosnia to West Africa, she has witnessed tragedy. But the photo of two drowned Salvadoran refugees this week still left Corinne Dufka in shock.

“It’s horrific,” Dufka, an associate director at Human Rights Watch, says of the picture, which shows a father and his 23-month old daughter dead, face down in the Rio Grande. “Photojournalism is full of images which have illuminated the gravity of a situation, made it less possible to ignore it or spurred both ordinary people and policy makers to action.”

In a world of unremitting information and video-driven chaos, the still photograph is an older and perhaps seemingly limited medium. But a solitary, silent shot can make remote news feel urgent and personal.

The deaths of Óscar Alberto Martínez Ramírez and his daughter Valeria, documented in an image made by journalist Julia Le Duc and distributed by The Associated Press this week, became an instant, singular moment in the immigration debate.

The power of still images

Other images not only recorded history, but helped make it. Karen Irvine, curator of Chicago’s Museum of Contemporary Photography, cites pictures of police tear-gassing civil rights protesters. Timothy B. Tyson, author of “The Blood of Emmett Till,” says the grotesque image of the black teenager murdered in 1955 by whites in Mississippi was a crucial part of the civil rights movement.