When U.S. president Donald Trump flew unannounced to Iraq for his first-ever overseas visit with American troops on Wednesday, the secrecy didn't last long.

Amateur plane-spotters tracked what they believed was Trump's Air Force One as it winged toward the Middle East under a false radio call sign. A photographer in the United Kingdom snapped a photo of the unmistakable, blue and white 747 jetting overhead, confirming the spotters' suspicion.

The cat was out of the bag. Trump was on his way to Iraq. And civilian sleuths had demonstrated, once again, the power of readily available tools to reveal covert military operations.

In recent years the combination of the internet, cheap satellite imagery, powerful consumer cameras and the information demands of a global economy have given interested amateurs many of the same tools that, just a few decades ago, were the exclusive purview of military intelligence agents and government spies.

Taking advantage of plane- and ship-tracking websites, commercial satellite imagery, internet forums for aviation photographers and other social media, these amateurs have become a new kind of hybrid journalist and spy. They call their practice "open-source intelligence," or OSINT.

OSINT practitioners claim they're keeping people informed and holding government accountable. “We the people shouldn't be the adversary that the government is hiding their actions from,” Steffan Watkins, an independent imagery expert from Canada, told The Daily Beast.

Governments predictably are less charitable. “Sharing seemingly harmless information online can be dangerous to loved ones and your fellow Marines—and may even get them killed,” the U.S. Marine Corps warns in its official handbook for social media use.

“Loose tweets destroy fleets,” the U.S. Air Force advised in 2015.

The case of Trump's flight to Iraq is indicative of the tools available to these civilian detectives. Twitter user @ETEJSpotter, who describes themselves as “tracking military movement over central Germany,” apparently was one of the first to notice a plane early on Dec. 26 leaving Andrews Air Force Base in Maryland, home of the U.S. Air Force's presidential transports.

The mysterious flight was plainly visible on each of several public websites that, for safety purposes, keep tabs on aircraft via their radio transponders. Similar sites also allow users to track ships at sea via their own transponders. Some hobbyists use these sites to zero in on particular ships and planes and listen to their radio broadcasts.

The plane from Andrews carried what @ETEJSpotter suspected was a false civil registration number and equally fictional radio call sign implying it was a civilian cargo flight. British photographer Alan Meloy soon confirmed that suspicion. Shooting skyward with a Canon digital camera sporting a 400-millimeter lens, Meloy captured a clear image of Air Force One cruising tens of thousands of feet overhead.

He tagged the photo with the plane's fake call sign and uploaded it to the image-sharing website Flickr. @EJETSpotter tweeted his suspicion and Meloy's visual confirmation. In short order, sleuths also spotted the other Air Force planes traveling along with Air Force One. The world knew the details of Trump's visit to Iraq hours before the White House intended.

"#OpSec anyone?" tweeted Paul Rieckhoff, founder of the advocacy group Iraq and Afghanistan Veterans of America, using the abbreviation for “operational security.”

Other examples of open-source intel abound. In 2011, NATO air operations over Libya were for a brief period plainly visible to internet users after several plane crews forgot to switch off their transponders.

Three years later, British blogger Eliot Higgins and his associates at the website Bellingcat meticulously assembled photographic evidence of Russia's involvement in the 2014 shoot-down of a Malaysian airliner over Ukraine that killed 298 people.

In November, Catherine Dill, a researcher with the Middlebury Institute of International Studies at Monterey in California, scoured commercially-available satellite imagery from San Francisco-based Planet Lab in order to count Chinese submarines—and determined that the Chinese navy likely possesses more nuclear-armed ballistic missile subs than analysts previously believed.

After Russian forces seized several Ukrainian navy boats and arrested their crews, the U.S. Air Force in early December deployed an observation plane to Ukraine in what the Pentagon described as a display of America's support for the government in Kiev.

Watkins, the Canadian imagery expert, tracked the American aircraft's flight path and revealed that, in fact, the plane never flew anywhere near Russian forces along Ukraine's periphery. “I have no reason to believe there was any display of anything coming from that flight,” Watkins told The Daily Beast.

The examples above reflect accurate and successful OSINT investigations. But Tom Cooper, an aviation journalist and author of Moscow's Game of Poker: Russian Military Intervention in Syria, 2015-2017, cautioned against believing everything that civilian sleuths claim.

There are limits to the OSINT practice, Cooper warned. “I did try to follow the work of diverse geo-locators—and gents discussing sat-imagery on Twitter, for example, or on Facebook—early while working on my book about the Russian intervention in Syria,” Cooper told The Daily Beast. “However, when cross-checking their data with those obtained from my first-hand sources, it turned out the tweeters simply have no clue what is going on.”

“Sat imagery,” or satellite imagery, Cooper added, “is no replacement for HUMINT,” or human intelligence. That is, an observer on the ground.

But many contributors to OSINT investigations are direct observers. In 2011, an I.T. consultant in Abbottabad, Pakistan live-tweeted helicopters flying over his house, unwittingly revealing the U.S. military raid that killed al Qaeda founder Osama Bin Laden at his nearby hideout.

More recently, the military hardware blog The Drive used ship-tracking software and photos posted by curious social media users to track U.S. Special Operations Command's secretive mother ship Cragside, a floating base for U.S. Navy SEALs and other commandos.

OSINT works so well that, even as it warns against service members accidentally providing data to the sleuths, the U.S. military takes advantage of its enemies' own online disclosures. In 2015, Gen. Hawk Carlisle, then commander of the U.S. Air Force's Air Combat Command, described his airmen using social media to target Islamic State militants.

“The [airmen are] combing through social media and they see some moron standing at this command,” Carlisle said. “So they do some work, long story short, about 22 hours later through that very building, three JDAM [satellite-guided bombs] take that entire building out. Through social media. It was a post on social media. Bombs on target in 22 hours.”

Having successfully tracked Trump, civilians sleuths aren't slowing down. “Right now I'm watching the position of a ship, and their movement, with a high degree of precision, on the other side of the planet,” Watkins said. “The ship is transmitting its location to all ships around it, and it's being received by a shore station, with an internet connection, which is feeding those VHF [radio] transmissions to 'the cloud'—MarineTraffic.com in this case—where I see them, and so does everyone else.”

If the ship were military and its crew wanted to hide its activities, the sailors simply could turn off the vessel's transponder and cease radio transmissions. That would limit Watkins' ability to directly track the ship. “I don't have access to synthetic aperture radar at high resolution, high-res multi-spectral satellite imagery, phone taps, moles, rats, etc.”

But going dark and silent comes at a cost to the crew, which might rely on the same ship-tracking website that Watkins does in order to safely navigate crowded waters. And besides, the stealthy vessel still might appear in commercial satellite imagery or in photos on Flickr, Twitter or Facebook.

These days information abounds, whether it’s about a nighttime commando raid, a countrywide air campaign or a secretive presidential trip. And it’s getting harder to stop a determined amateur from gathering and analyzing the info. “The best I can do is try and piece together the facts with the available information,” Watkins said, “which is ripe for the picking, if you know where to look.”