Adding a captcha security to a google form

I have a Google form, designed for data collection (collecting entries for a sweepstakes), and I need to install a captcha widget or whatever it is called to protect against spam. I have already signed up with Captcha however I do not know how to install it basically. I have been looking around and have found that for the experienced programmer it may not be that hard to do. Please help, would like to get this done as soon as possible.