Well, one way is to have a form input hidden by css, that is like spam catching 101. I actually found a fairly interesting sort of captcha I am using for signi

Well, one way is to have a form input hidden by css, that is like spam catching 101. I actually found a fairly interesting sort of captcha I am using for signing of rental agreements using jsignature which draws a canvas that people can sign using their mouse. This updates a hidden form element with mouse x/y data to draw the signature again if you need to. You could potentially use something like this, but reCaptcha is incredibly easy to integrate.