But the white sensor could still be used. I envision the robot as having a hopper. When something white was dropped in, the robot would sense it and dispense a tiny pellet of food.

A group of young grows would be taught how the machine works. They could find something white and drop it in, then receive food. When done, the robot could be parked in various area, and the crows would scour the surroundings to put trash into it.

I suspect that wild crows would pay attention and learn this way as well. Crows have culture. Ultimately, cities could be kept clean by their resident crows and a few robots full of kibble.