A United Nations photograph showing a sea of hungry Palestinians awaiting emergency food amid the detritus of their bomb-ravaged neighborhood near Damascus has been retweeted more than eight million times in the past few weeks, becoming such an arresting image of the Syrian civil war that some blogosphere skeptics have suggested that it was digitally faked. The suggestion provoked a passionate denial on Tuesday by the official responsible for distributing the photo.

The official, Chris Gunness, the spokesman for the United Nations Relief and Works Agency, which administers aid to Palestinian refugees in the Middle East, said he was stupefied by the expressions of doubt about the photo. At the same time, Mr. Gunness said, the skepticism may partly reflect a blindness by many people to what is happening in Syria, which entered its fourth year of war this month.

“The photo is an exact replica of reality,” Mr. Gunness said in a telephone interview from Jerusalem, where he is based. “I can understand why that reality would beggar belief. But in the 21st century, such a scene exists. People are incredulous because it’s hard to believe.”

Mr. Gunness, who has expressed personal outrage at conditions at the Yarmouk camp, chose the photograph to represent the suffering in Syria as part of a social media campaign known as a Thunderclap. The campaign, by 130 humanitarian relief organizations, including major United Nations agencies, is pressing for access to Syrian civilians trapped in fighting between President Bashar al-Assad’s loyalists and insurgents.