the post office used humans for many years to train OCR models, e.g. zip code readers.

I visited a postal routing facility once in the 90s and saw a long row of metal stationed by about 20 people, 10 to each side. Envelopes passed through on a sort of pneumatic tube-like conveyor, paused in front of a human operator who read a single digit of a zip code, keyed it in and sent the envelope to be read by the next person.