I think its pretty clear the reading books bit was abandoned long ago. I never get non-test words that are in any way a struggle for a competent OCR system. And on the occasion that I do, its impossible for me to read either. If they provided context it would be much more helpful.
As an aside, if you've ever had to solve one of these through TOR and you happen to be running through some eastern european countries... good god those are the most frustrating captchas I've ever seen. Long strings of "mnnmrnrmnm" with contrasting colors and jpeg artifacts... a few attempts at solving those makes me want to kill someone. I feel bad for people trying to do anything on the internet from those countries. I wonder what the rationale is for making captchas nearly impossible to solve in specific regions.