This seemed like the only appropriate thread for this feedback:
I had to refresh about 10 times in registration before I got a clock captcha that was actually decipherable. In the rest of them, the actual lines for the clock hands were completely or near-completely obscured by the other random garbage lines. Maybe my eyesight is just really bad, but this is by far the most frustrating captcha I've ever seen. Maybe false bot positives are okay in this case and you'd rather drive away users if it keeps the bots out - could make sense if you get tons of bots - but I figure maybe some minor changes to the settings for that captcha could make it a little more reasonable.
In particular a few of the themes for the clock make the hands indecipherable from the noise lines. When you get a clock theme where the hands actually look like clock hands, it's not as bad - you just need to figure out which one is the hour and which is the minute (sadly, this is not simple either - in some themes they seem to be almost exactly the same length...)