Due to all of the objections to Captcha technologies and
general user disdain, I finally just put a question on my form that
says "What is the opposite of cold". If the entry equals "hot" then
the form continues.
Looking at my web logs, the spammers/bots are not smart
enough to actually READ the questions, and therefore never populate
the answer with the word "hot".
Give it a try. If it does not work, go to something more
sophisticated. Use your imagination with the question. You will
likely have to tailor it to your audience and make it simple enough
to where there is conceivably only one answer. You might consider
just saying "Enter 'yes' if you want to continue".
Sometimes the simplest solution really is the best
solution.