I read every page on the website, but it doesn't say anything about what I want to know, except this, which is peripherally related:
Our service also includes IP address filtering and detection. If we determine that a given IP address is successfully solving too many CAPTCHAs in a certain period of time, the address is immediately flagged for review.
So presumably when I go on one of my retagging sprees, the system sits up and pays attention. However, even days later of little activity, I've been getting more difficult-to-type words, regardless of the frequency I hit the captcha.
I started with only easy words like 'with', 'and', etc., but now I'd say half the time it's giving me long/difficult-to-type words like 'congressional' (that's the only one I remember from my session a few minutes ago).
Am I imagining this, or are the words actually supposed to be more difficult as time goes on? I'd be particularly interested to hear from some high-rep users who have done a lot of manual retagging.
(Yes, this is a bit of a whine post, but this, combined with the low captcha threshold, is making it more time-consuming and annoying for me to do retagging, which really detracts from the job I want to do.)
Edit: Here is a sampling of the captchas I got during my recent retagging session just now. These are pretty easy ones compared to some I've seen.