Not any more, the Blackbird aka SR71 was retired from service some years ago. Not likely that we'd send a U2/TR1 over such hostile territory, so my guess is some of the fine, fine, fine Keyhole imagery. Given the bellicosity of the N. Koreans, I'm betting we have a fleet of KHs covering every square inch of that dismal country.
Without going into a lot of details on system capabilities, let me say that the H-camera and ASARS can cover virtually all of North Korea from Pyongyang to the DMZ. If these mines disappeared from a DPRK naval base, they were probably observed at Nampo or Wonsan, North Korea's major naval facilities on the Yellow Sea and Sea of Japan, respectively.
But the story's still a little fuzzy, in a couple of respects. First, acoustical mines are relatively small, and wouldn't be observed on imagery unless they were placed outside a known storage facility, or observed in a distinctive shipping container associated with that type of weapon. Unique or distinctive shipping containers are often our first tip-off to the shipment of larger items, such as aircraft components, missile sections, etc. I was never an imagery analyst or a naval specialist, so I'll defer to anyone who knows more about the imagery signature of naval mines. However, it would be difficult to detect such a shipment unless the mines were in the open in large quantities, or (the other possibility) we got some other intelligence that cued the imagery systems to begin looking for the mines.
One more thought: if we can trace this shipment to one of bin Laden's boats, it needs to be boarded, searched and sunk immediately. It's also worth noting that another, troublesome, Middle Eastern country makes regular flights to North Korea to pick up weapons. I hope our intel folks are watching that country, to see if they made a pick-up for Osama and the boys.