It was the same when this was about words from old books. I always had to fill in letters the average person would have thought it to be, not what it actually was (e.g. the letter "f" for what really was an "s" in gothic type).

Nowadays it's much easier, you can click anything that looks vaguely the same (e.g. boxy things for cars, ads for traffic signs, traffic signs for store fronts etc.). The fact that it's so easy to poison the training set makes me very wary about the autonomous car future...