Not mentioned is that it actually does have something to do with security, because once enough users have transcribed a word, in addition to it being returned t

Not mentioned is that it actually does have something to do with security, because once enough users have transcribed a word, in addition to it being returned to the digitization project, it can be used for future CAPTCHAs as a known word. According to Wikipedia, this was at least historically the case for reCAPTCHA.