Leads: Reject Leads That Don’t Use reCAPTCHA
Where: This change applies to Salesforce Classic and Lightning Experience in Group, Professional, Enterprise, Performance, Unlimited, and Developer editions.
How: In Setup, go to the Web-to-Lead Setup page, and look for the Require reCAPTCHA Verification setting. Enabling this setting turns on the Include reCAPTCHA in HTML setting on the Create a Web-to-Lead Form page. Then make sure that the HTML on your website includes the reCAPTCHA code.
In new orgs, Require reCAPTCHA Verification is enabled by default.