Bots are much more intelligent nowadays. Spammers easily send a lot of spam email using bots if you use captcha free contact form. reCaptcha, a simple but yet unreadable for bots can save your inbox from spam mail.
reCaptcha comes with weForms. With it, you can easily keep your form submission safe from spammers.
Adding reCaptcha to A Form
If you like to add reCaptcha on your contact form, please navigate: wp-admin → weForms → Settings → Insert your reCaptcha Site key and Secret Key, and Save them. [Simply generate your API Keys if you don’t have yet]
Now, navigate to wp-admin → weForms → All Forms → edit/create a form → drag & drop the reCaptcha field from others section to your form area.
Related: How to create a form.
Add the field level & save the form.
Here is the preview!