hat appears mundane to the untrained eye can offer surprising insights to the independent analysts tracking North Korea's military capabilities.

The flow of information out of the country is notoriously thin, so experts often turn to open-source material for clues. That's especially true for those operating outside government in the so-called parallel intelligence community.

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Jeffrey Lewis and his team at the Middlebury Institute of International Studies here have spent years studying satellite imagery, military parades and propaganda hoping to glean revealing tidbits and understand the latest developments in North Korea.

For example, the serial number of a missile-bearing crane recently helped Lewis to deduce a weapon's range — leading him to believe it could likely hit the mainland U.S.

A photo released by North Korea showing its most advanced intercontinental ballistic missile allowed Lewis' team to identify the crane's manufacturer and its model. Searching online, they found the crane's length and load capacity — which allowed them to infer the missile's weight and range.

Kim Jong Un's regime tested that missile in November. Had it been fired at a lower angle, some experts believe that it may have had a range of 8,100 miles, placing the continental U.S. within reach.

Pyongyang's own videos also allow Lewis to measure any launched missile's size and speed — two variables that reveal the power of its engine. From there they model the missile's performance, so even if launched vertically, they can project whether it could potentially reach New York or Los Angeles.

Lewis' team has also poked holes in North Korean claims of prowess. A video released in January 2016 purporting to show a successful missile launch via submarine was actually two different launch videos spliced together. The submarine launch was really a failure: The missile exploded after ignition. But the official video cut to footage from a successful Scud missile launch from June 2014 and claimed success.

However, open-source analysis has its limits.

"The intelligence community has access to the best satellites in the world from radar to thermal to multi-spectral," explained Joseph S. Bermudez Jr., a senior analyst at 38 North, a project affiliated with Johns Hopkins University that analyzes North Korea. Government officials also have access to signals intelligence and sources around the world.

"You're talking about hundreds of thousands of people in the intelligence community working on an issue, as opposed to half a dozen," Bermudez said. "There's a level of difference."

In September, North Korea conducted its sixth nuclear test and its first of a miniaturized hydrogen bomb, intended for a long-range missile.

Mounting a nuclear warhead on a long-range ICBM is North Korea's next challenge. But Lewis says it's a question of when, not if, Pyongyang will get there.

More on MSNBC's 'On Assignment with Richard Engel' Friday at 9 p.m.