Global surveillance
Let's look at this realistically. The only time you can have 100% surveillance on a location is if you have a satellite in a geostationary orbit above what you're interested in, and you have clear skies.
Generally speaking, surveillance satellites are in polar or highly inclined orbits, so that they can cover the maximum amount of the Earth's surface. But what this means is that they only pass over one particular area periodically, typically twice in any 24 hour period.
So, a particular satellite may not have captured any images of MH370, although if you had access to all of the pictures from every global surveillance platform, you may be able to capture a few images of the plane, but it probably depends on the cloud cover at the time.
What the security forces are interested in are quite often relatively static, so being able to see them once per day (assuming one pass is at night) is often enough to get some idea what is going on. Large balloons, being relatively slow (although I guess this depends on the altitude), are probably quite easy objects to follow. Planes, not so much.
Biting the hand that feeds IT
