[InclinedPlane]

beats ... I hope that was intentional.

Seriously though, you're right, even if it requires a human in the loop it's still a huge benefit. Farms could even use remote workers to do the identification.

[Splines]

This seems like the easiest way to get it working now. In fact, you could do the inverse at some point in the crop cycle - get workers/robots to identify the viable crops, and from that point on stamp everything else remotely plant-like out.

[Animats]

Humans are too slow. If this can be done at all, it can be done far faster than a human can do it.