SEOUL, South Korea — April has not been a great month for North Korea’s image-makers.


First, they invited dozens of journalists to chronicle the 100th anniversary of the birth of the country’s revered founder, Kim Il-sung, only to see their signature event — the launching of a satellite — go bust.


Now, a pair of German missile experts have gone public with evidence suggesting that new missiles that the North rolled out with much pomp at a parade just days later were mock-ups, and clumsy ones at that.


After a close analysis of photographs from the parade, the missile experts, Markus Schiller and Robert Schmucker, found what they said were tell-tale signs of fakery. The warhead’s surface, they wrote in a paper posted on a respected arms control Web site, is undulated, “as if a thin metal sheet was fixed onto a simple inner frame.” The missiles were slightly different from each other, with covers mounted horizontally on one missile and vertically on another, and they did not even fit the launchers they were carried on, the analysts said.


“It is therefore clear that the presented missiles are only mock-ups of low quality,” they wrote in a post on the Web site, armscontrolwonk.com. “It remains unknown if they were designed this way to confuse foreign analysts, or if the designers simply did some sloppy work.”


One thing is clear, they said. There is still no evidence that North Korea has a functional intercontinental ballistic missile, and the parade was just “a nice dog and pony show.”


Military mock-ups are nothing new. Analysts believe some of the missiles Iran has trotted out during its own weapons parades are just copies. And when South Korea used to host its own military parades, some of the weapons were widely believed to be imitations.


But if North Korea believed it could gain some strategic leverage over Washington through its display of new missiles, it needed to do a better job of covering its tracks, the analysts said.


Still, security experts said, Westerners taking solace from the analysts’ report should exercise caution.


John Park, a research fellow at Harvard University’s Belfer Center, warned that the reports about fake missiles should not cause people to underestimate the expansion of North Korea’s missile program. He said the country had gained formidable procurement capabilities through growing commercial ties between its state-run trading companies and private Chinese companies. The rapid modernization of China’s military also has created a growing stockpile of old military hardware.


“Such supplies like old missile parts have a tendency to go ‘missing’ as commercially motivated elements meet the demand from countries like North Korea,” Mr. Park said. Such concerns appeared to be borne out when analysts suggested that the 16-wheeled vehicles that carried the missiles in the April 15 parade apparently originated from a state-run Chinese company.


Other analysts also warned that the mock-ups could simply be copies of real missiles being developed. One of the West’s greatest fears is that North Korea will eventually develop a powerful enough missile to loft nuclear warheads as far as the United States.


The art of false impressions has a storied history in North Korea. It built Potemkin propaganda villages along the border with the South during the cold war when it still believed that it could trick South Korean soldiers to defect to the “socialist paradise” the villages represented. And North Korea’s state-run news media were believed to have sent out doctored photographs of Kim Jong-il, the nation’s leader then, in an apparent attempt to make him look less ill than he was after a stroke in 2008.


If the missiles, larger by far than earlier incarnations, convinced people of their new leader’s bona fides — then they may have been a wild success, at least by Pyongyang’s standards.