[lorenzhs]

"the human eye can barely see the lander" is a bit exaggerated. It's not immediately obvious where in the image the lander is (it took me a few seconds to find it), but well visible once you've got the position.

"Considering that the chances of losing these landers is not that low" - most of the time, when the mission fails, they don't make it to the surface, though. As far as I know, Beagle 2 is the only lander that was lost and later found. The Mars Polar Lander likely dropped onto the surface from some 40m up, maybe a wreckage could be found there. But other than that, I'm not aware of any landers that could be found with a camera in orbit. Debris is hard to find, even on earth - it took over 20 hours to find a crashed fighter jet in Switzerland last week, and another day to find the pilot's body.