I think the beauty of reCAPTCHA is that if there's stronger OCR, those algorithms can be integrated into Google's book digitization system, resulting in a new v

I think the beauty of reCAPTCHA is that if there's stronger OCR, those algorithms can be integrated into Google's book digitization system, resulting in a new version of reCAPTCHA that will only show words not recognized by this new algorithm. As a result, the captchas will get harder if there's better OCR. Of course eventually, OCR systems will become as good as a significant fraction of the population, and then the idea breaks down.