Hello,
I've installed this plugin and checked all the various settings, but for some reason the Captcha looks like it's displaying twice.
Have a look at the screenshot:
http://seanbelly.com/tester/reCaptcha.png
It does make it extra hard for spammers, but unfortunately us humans can't use it either.
http://wordpress.org/extend/plugins/contact-form-7-recaptcha-extension/