SHANKSVILLE, Pa. , Sept. 7 — Valencia M. McClatchey thought she was doing the right thing when she gave the F.B.I. a copy of her photo of the mushroom cloud that rose over the hill outside her home after United Flight 93 crashed in a field here on Sept. 11, 2001.

And, after it became apparent that hers was the only known picture of that ominous, gray cloud — and the first shot after Flight 93 crashed — she thought she was still doing the right thing when she gave copies to people who asked for them, and let newspapers and television stations use it.

But fame for the photo has had an unexpected cost for the photographer.

“Every time I’ve done any stories it goes online and all these conspiracy theorists start up and they call me and harass me,” said Mrs. McClatchey, 51, who runs her own real estate company.

In numerous online postings, critics have ripped apart every element of the photo, and Mrs. McClatchey’s life. They accuse her of faking the photo, of profiteering from it and of being part of a conspiracy to cover up the fact that Flight 93 was shot down by the government.