Welcome to Findnerd. One of the most used plugin named custom form7 which is useful to manage the contact us page of the website. We need to show the captcha in contact us form. If you start the customization in contact form 7 then it is very long process to understand the flow of coding in plugin. We can simply install the plugin named Really Simple CAPTCHA which is specially for contact form7 plugin. It will fullfll your requirement without make changes in the plugin. Kindly download the plugin from below link.