I have a WordPress site with a form that I need to add a captcha to. The form isn't it's own template or even on it's own page but it is a single php file that is included on all of the pages. The actual form is in the shape of a drop down menu. When a user clicks on the "request info" link, the form drops down from the navbar. Do to the way it is set up I can't use a WordPress plugin.
Normally, I could I just add a php captcha script and be done with it but the form action is set to post to an external website. When the visitor submits the form, it goes to another website that collects the info, as you can see here:
<form action="https://www.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8" method="POST" name="contact" id="contact" onsubmit="return checkform(this);">
Because the form isn't verified with a php file on the sites server, I don't know how to verify the captcha and get it to work. Does anyone have any suggestions?