MarkT:
Now if each ping pong ball had an LED in it and the lights were off you might be able to
find them without resorting to OpenCV and major-league hardware.
Color detection actually wouldn't be difficult, as long as there weren't any other whitish objects. Color sensing modules are cheap. Not sure what the range on those things are, and it may still be a blind wander until one happens to fall into range before detection runs. But after I typed all of this so far I think we're talking the difference between 'finding' and 'identifying as a ball once found'. So I'm not disagreeing with you after all.