Allowing the person that writes the answer to submit a link is problematic, IMHO. Of the 3 I tried, 2 said "I love you" and linked to Glenn Beck. I personally dislike Mr. Beck very much, and that alone would keep me from using this on any project.

You are going to run afoul of people just as easily if someone links to Keith Olbermann, or a site about Gay Rights, or kicking out immigrants, or atheism, or the KKK, or [insert inflammatory thing here].

The whole reason for captcha's is so someone can't put arbitrary links on YOUR site, embedding your anti-captcha solution just makes sure they are always in the same place. No thanks, I'll just use ReCaptcha.