Regarding
http://en.wikibooks.org/wiki/Special:Captcha/help :
it says "Please contact the site administrators for assistance if this
is unexpectedly preventing you from making legitimate posts." but
doesn't have a button to do so.
Anyway, e.g., I have images turned off in my browser, so come up with
a word quiz.
Hmm, wikibooks not wikipedia? OK sorry.