Top 14 Form Usability Tips

12. CAPTCHA

JUST SAY NO!!

Captcha V2

W3C Inaccessibility of CAPTCHA (including V3)

Developer's Guide to Invisible ReCAPTCHA

ReCAPTCHA demo - Google

Get reCAPTCHA v2

Effective alternatives to inaccessible CAPTCHAs - mostly

CAPTCHA-less Security – Karl Groves

Spam-free accessible forms