Kent Kobersteen, former Director of Photography of National Geographic "The pictures are by Robert Clark, and were shot from the window of his studio in Brooklyn. Others shot the second plane hitting the tower, but I think there are elements in Clark's photographs that make them special. To me the wider shots not only give context to the tragedy, but also portray the normalcy of the day in every respect except at the Towers. I generally prefer tighter shots, but in this case I think the overall context of Manhattan makes a stronger image. And, the fact that Clark shot the pictures from his studio indicates how the events of 9/11 literally hit home. I find these images very compelling—in fact, whenever I see them they force me to study them in great detail."

On September 11, 2001, photography editors across the world, overcome with a deluge of devastating imagery, faced the daunting task of selecting photos that would go on to define a catastrophe like no other. A decade later, TIME asked a wide variety of the industry's leading photo editors, photographers, authors, educators, and bloggers to tell us which image moved them most—and why.

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Some couldn’t choose one single image. Vin Alabiso, head of photography at the Associated Press on September 11, 2001, said, "Of the thousands of images that were captured, I thought only a handful would truly resonate with me. I was wrong. As a document of a day filled with horror and heroism, the collective work of so many professionals and amateurs leaves its own indelible mark on our memory."

Holly Hughes, editor of Photo District News, said she was moved most by the photographs of the missing people that blanketed the city in the days after 9/11. "The images that can still move me to tears are the snapshots of happy, smiling people looking out from the homemade missing posters that were taped to signposts and doorways and mailboxes," she said. "How those posters were made, the state of mind of the people who stood at Xerox machines to make copies, it's too painful to contemplate. Those flyers stayed up around the city for weeks, through wind and rain, and became entwined with the sorrow and anxiety we carried with us day after day."

(Related : Revisiting 9/11: Unpublished Photos by James Nachtwey )

Alabiso added, "A decade later, I could only wish that the most memorable photo of September 11, 2001, would not have been memorable at all...simply two towers silhouetted against a clear azure-blue sky."

To visit TIME’s Beyond 9/11: A Portrait of Resilience, a project that chronicles 9/11 and its aftermath, click here .