WASHINGTON — Governments have long prized intelligence gleaned by spies, satellites and wiretaps. But senior intelligence officials said key findings in a new intelligence report on Iran’s nuclear weapons hinged on intelligence that was hidden in plain sight — on the Web, in newspapers and in nongovernmental reports.

The National Intelligence Estimate on Iran’s nuclear weapons program released Monday relied in important ways on pictures of Iranian nuclear sites snapped by reporters during government tours of the facilities. The first was in March 2005. At the time, a U.S. State Department spokesman derided the visit as a “staged media tour.” Two years later, Iran opened a different facility to the press.

“We actually ended up with photography of all of the equipment there. So instead of having very extensive arguments about whether pipes were 12 inches in diameter or 12 centimeters, we have data,” a senior intelligence official told reporters Monday.

He called the visit “astounding.” The official spoke only on condition of anonymity because of the sensitivity of the subject.

“That helped us understand what they had and might be capable of as well,” he said.

Those photos, along with unclassified reports from the International Atomic Energy Agency and intelligence gathered in clandestine ways, make U.S. intelligence agencies predict “technical problems” will prevent Iran from being able to produce enough enriched uranium to fuel a nuclear warhead for at least two years. The State Department’s intelligence office believes the enrichment would not occur for at least five years because of “foreseeable technical and programmatic problems.”

Jeffrey Lewis, director of the Nuclear Strategy and Nonproliferation Initiative at the New America Foundation think tank, found the admission remarkable.

“If the press hadn’t taken those pictures does it really mean they would not have had that?” he said. “It’s really curious.”

Another intelligence official said the 2005 photos were not factored into that year’s intelligence estimate on Iran because the photos were not available to them then.

Some analysts believe publicly available information — known as “open-source intelligence”— is inherently untrustworthy, released by a government to deliberately mislead.

“If you have a photo in March ‘05 that was somehow anomalous to other intelligence you had, you would think the photo was a deception,” said Mark Lowenthal, a former assistant CIA director for production and analysis, now the president of the Intelligence and Security Academy, a training and consulting company. “As you start doing more collection, you start getting other intelligence, and say, ‘Oh my god, that photo was real.’ “

Lowenthal doubts the photos themselves made a critical difference on their own.

“We don’t have a lot of ‘Aha’ moments in this business,” he said. “We have small accretions of information.”

Principal deputy national intelligence director Donald Kerr said Thursday at a House intelligence subcommittee hearing that the Iran report was perhaps the most deeply sourced National Intelligence Estimate ever. The document has over 1,000 footnotes, he said.

Open-source intelligence generally makes up between 80 percent and 90 percent of the information analysts use in their reports. But it has fallen in and out of fashion, and the cultural obstacles to its use inside intelligence circles can be high.

“There’s an inherent bias in the mid-generation (of analysts) toward believing there is greater credibility in classified information,” David Shedd, the deputy director of national intelligence for policy, plans and requirements, told the subcommittee.

“It used to be this use of this kind of material was not valued much because it wasn’t secret,” agreed Arthur Hulnick, who worked at the CIA for 28 years and is now a professor at Boston University. “Policymakers used to say, ‘Don’t give me something I can read in the New York Times. I want something sexier than that.’ “

Hulnick’s students have written their own assessments of Iran’s nuclear program using only open sources. He said their conclusions are similar to what the U.S. intelligence agencies just produced.

U.S. intelligence agencies are increasingly incorporating open-source intelligence into their work, lured by the vast amount of information now available online and in specialized publications.

“People are using it. They are seeing the value now,” Kerr said.

Open source has become especially vital in the last few years because so many intelligence assets have been shifted to force-protection missions, the senior intelligence official said.

“That means other forms of collection that used to dribble automatically to your computer aren’t there. You need to go elsewhere to get that” information, he said.

In November 2005, the director of national intelligence unveiled the Open Source Center, a digital and physical library created to organize everything the intelligence community discovers and knows to be reliable. The official said it is in the early stages of ingesting information and vetting it with experts.

Still, barriers remain, the official said. Some intelligence officers still do not have Internet connections at their desks. And there are “excessively cumbersome” rules governing contact with outside experts that limit where analysts can turn for additional information, fearful they would tip off an enemy to U.S. intelligence interests, he said.